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1.  Congenital cerebral palsy and prenatal exposure to self-reported maternal infections, fever, or smoking 
American journal of obstetrics and gynecology  2013;209(4):332.e1-332.e10.
OBJECTIVE
The objective of the study was to investigate the association between maternal self-reported infections, fever, and smoking in the prenatal period and the subsequent risk for congenital cerebral palsy (CP).
STUDY DESIGN
We included the 81,066 mothers of singletons born between 1996 and 2003 who participated in the Danish National Birth Cohort. Children were followed up through December 2008. Information on maternal infections, fever, smoking, and other demographic and lifestyle factors during pregnancy were reported by mothers in computer-assisted telephone interviews in early and midgestation. We identified 139 CP cases including 121 cases of spastic CP (sCP) as confirmed by the Danish National Cerebral Palsy Register. Cox proportional hazards regression models were used to estimate adjusted hazard ratios (aHRs) and 95% confidence intervals (CIs).
RESULTS
Self-reported vaginal infections were associated with an increased risk of CP and sCP (aHR, 1.52; 95% CI, 1.04–2.24; and aHR, 1.73; 95% CI, 1.16–2.60, respectively) and particularly untreated vaginal infections were associated with an increased risk of sCP (aHR, 1.95; 95% CI, 1.16–3.26). Fever was associated with the risk of CP (aHR, 1.53; 95% CI, 1.06–2.21). Smoking 10 or more cigarettes per day during pregnancy was also associated with sCP (aHR, 1.80; 95% CI, 1.10–2.94). There was a modest excess in risk for children exposed to both heavy smoking and vaginal infections. No other self-reported infections were significantly associated with CP.
CONCLUSION
Self-reported vaginal infections, fever, and smoking 10 or more cigarettes per day during pregnancy were associated with a higher risk of overall CP and/or sCP.
doi:10.1016/j.ajog.2013.06.023
PMCID: PMC4512233  PMID: 23791566
congenital cerebral palsy; maternal infections; pregnancy; smoking
2.  Risk of Fetal Death after Treatment with Antipsychotic Medications during Pregnancy 
PLoS ONE  2015;10(7):e0132280.
Background
Antipsychotic medications are increasingly used during pregnancy. Nevertheless, fetal risks are still not fully studied. It is currently unclear whether the antipsychotic treatment might induce a higher risk of fetal death. We aimed to determine if use of antipsychotic medication during pregnancy is associated with an increased risk of spontaneous abortion or stillbirth.
Methods
In a historical cohort study, we identified all clinically recognized pregnancies registered in the nationwide Danish registries from 1997 to 2008 (N = 1,005,319). Exposure was defined as any prescription of antipsychotic medications redeemed by the pregnant women during the exposure window, and recorded in the Danish National Prescription Register. Outcome was defined as any spontaneous abortion or stillbirth recorded in the Danish National Hospital Register and the Danish Medical Birth Register respectively.
Results
Women exposed to antipsychotic medications during pregnancy had a 34% higher risk of spontaneous abortion (adjusted relative risk = 1.34; 95% confidence interval = 1.22; 1.46) compared to unexposed women, but a similar risk compared to women exposed prior to (but not during) pregnancy (adjusted relative risk = 1.04; 95% confidence interval = 0.93; 1.17). The risk of spontaneous abortion was not increased in exposed pregnancies when compared to unexposed pregnancies in the same women (adjusted hazard ratio = 1.11; 95% CI = 0.94; 1.31). A twofold higher risk of stillbirth was found in women exposed to antipsychotic medications compared with unexposed women (relative risk = 2.27; 95% confidence interval = 1.45; 3.55) and compared with women exposed only prior to pregnancy (relative risk = 2.06; 95% confidence interval = 1.01; 4.19).
Conclusions
The increased risk of spontaneous abortion found in women treated with antipsychotic medications during pregnancy is most likely due to confounding factors. The risk of stillbirth was twofold higher in pregnancies exposed to antipsychotic medication during pregnancy. Treatment with antipsychotic medications during pregnancy requires careful consideration.
doi:10.1371/journal.pone.0132280
PMCID: PMC4498617  PMID: 26162087
3.  Perfluoroalkyl acids and time to pregnancy revisited: An update from the Danish National Birth Cohort 
Environmental Health  2015;14:59.
Background
We previously demonstrated an association between plasma perfluorooctane sulfonate (PFOS) and perfluorooctanoate (PFOA) and longer time to pregnancy (TTP) in a sample from the Danish National Birth Cohort (DNBC, 1996-2002). In this study we investigated this association in a new sample from the same cohort.
Methods
Sample 1 consisted of 440 women, and Sample 2 consisted of 1161 women from whom we previously published the associations between PFOS or PFOA and TTP. We performed sample-specific and pooled analyses using discrete-time survival analyses to estimate fecundability ratios according to PFOS and PFOA quartiles, adjusted for potential confounders chosen guided by a directed acyclic graph. We also estimated odds ratios for infertility (TTP > 12 months or infertility treatment) according to PFOS and PFOA by multivariable logistic regression.
Results
In Sample 1 PFOS was not associated with lower fecundability ratios or infertility, and there was a tendency towards longer TTP with increasing PFOA only in parous women. In Sample 2 previously reported associations were again seen. In the pooled analyses including both parous and nulliparous women fecundability ratios were 13-22 % lower for the three higher quartiles of PFOS or PFOA compared to the reference quartile.
Conclusions
The pooled analyses were driven by the larger old sample, but we did not corroborate our previous finding of an association between high PFOS and longer TTP in the new sample. The tendency towards an association for PFOA and TTP in parous women may be due to reverse causation. Results from the new sample are more in line with the recent literature.
Electronic supplementary material
The online version of this article (doi:10.1186/s12940-015-0040-9) contains supplementary material, which is available to authorized users.
doi:10.1186/s12940-015-0040-9
PMCID: PMC4493954  PMID: 26148742
Female infertility; Fecundity; Reproduction; Perfluorooctane sulfonate; Perfluorooctanoate; Perfluorinated chemicals; Epidemiology; Humans
4.  Social Conditions for People With Down Syndrome: A Register-Based Cohort Study in Denmark 
Today, most persons with Down syndrome (DS) survive into middle age, but information on their social conditions as adults is limited. We addressed this knowledge gap using data from national registers in Denmark. We identified a national cohort of 1,998 persons with DS who were born between 1968 and 2007 (1,852 with standard trisomy 21, 80 with Robertsonian translocations and 66 with mosaicism) using the Danish Cytogenetic Register. We followed this cohort from 1980 to 2007. Information on social conditions (education, employment, source of income, marital status, etc.) was obtained by linkages to national registers, including the Integrated Database for Longitudinal Labor Market Research. For those aged 18 and older, more than 80%of persons with DS attended 10 years of primary school, with about 2% completing secondary or post-secondary education. About 4% obtained a full-time job, whereas the remaining mainly received public support from the government. Only a few (1–2%) of persons with DS were married or had a child. No significant differences in these social conditions were seen between males and females. More persons with mosaic DS attended secondary or post-secondary education, had a full-time job, were married, or had a child (18%, 28%, 15%, and 7%, respectively), compared with persons with standard DS (1%, 2%, 1%, and 1%, respectively). These data may provide families with better insight into social conditions and society with a better understanding of the social support needed for persons with DS.
doi:10.1002/ajmg.a.36272
PMCID: PMC4490827  PMID: 24273114
Down syndrome; mosaic trisomy 21; social conditions; offspring
6.  Disproportionate Fetal Growth and the Risk for Congenital Cerebral Palsy in Singleton Births 
PLoS ONE  2015;10(5):e0126743.
Objective
To investigate the association between proportionality of fetal and placental growth measured at birth and the risk for congenital cerebral palsy (CP).
Study Design
We identified all live-born singletons born in Denmark between 1995 and 2003 and followed them from 1 year of age until December 31st, 2008. Information on four indices of fetal growth: ponderal index, head circumference/ abdominal circumference ratio, cephalization index and birth weight/ placenta weight ratio was collected. Cox proportional hazards regression models were used to estimate adjusted hazard ratios (aHR) and 95% confidence intervals (CI). All measurements were evaluated as gestational age and sex specific z-scores and in z-score percentile groups, adjusted for potential confounders, and stratified on gestational age groups (<32, 32-36, 37-38, 39, 40, ≥41 weeks).
Results
We identified 503,784 singleton births, of which 983 were confirmed cases of CP. Head/ abdominal circumference ratio (aHR:1.12; 95%CI:1.07-1.16) and cephalization index (aHR:1.14; 95%CI:1.11-1.16) were associated with the risk of CP irrespective of gestational age. Birth weight-placental weight ratio was also associated with CP in the entire cohort (aHR:0.90; 95%CI:0.83-0.97). Ponderal index had a u-shaped association with CP, where both children with low and high ponderal index were at higher risk of CP.
Conclusions
CP is associated with disproportions between birth weight, birth length, placental weight and head circumference suggesting pre and perinatal conditions contribute to fetal growth restriction in children with CP.
doi:10.1371/journal.pone.0126743
PMCID: PMC4431832  PMID: 25974407
7.  Hospitalizations among persons with Down syndrome: a national cohort study in Denmark 
Summary
Background
Most persons with Down syndrome (DS) now survive to adulthood, but their health care needs beyond childhood are not well described. We examined hospitalizations among persons with DS in Denmark.
Methods
We followed 3,212 persons with DS (1910-2007), identified from the Danish Cytogenetic Register, and a random sample of persons without DS from the general population (as comparison group), through the National Hospital Register from January 1, 1977, to May 31, 2008. Poisson regression was used to calculate rate ratios for numbers of overnight hospital admissions and hospital days.
Findings
During this time period, persons with DS had more than twice the rate of hospital admissions and nearly three times as many bed-days as the population as whole. Malformations, diseases of the respiratory system, and diseases of the nervous system or sensory organs were the principal indications for hospital admissions. The higher rate ratios for hospital admissions were mainly seen among persons less than 20 years of age, and hospitalization for neoplasms or for diseases of the musculoskeletal system or connective tissue was much less frequent than expected among adults with DS. Persons with DS who had congenital heart defects were far more likely to be hospitalized than those without.
Interpretation
Persons with DS in Denmark are hospitalized more frequently and for more days than persons without DS; however, hospitalization usage differs by age (with a higher burden at younger ages) and by presence of a congenital heart defect. As survival among persons with DS continues to improve, these data are helpful for health care planning, although results may be different within other health care systems.
doi:10.1002/ajmg.a.35711
PMCID: PMC4415492  PMID: 23404922
Down syndrome; hospitalization; comorbidity; congenital heart defects
8.  Attention Deficit/Hyperactivity Disorder and Childhood Autism in Association with Prenatal Exposure to Perfluoroalkyl Substances: A Nested Case–Control Study in the Danish National Birth Cohort 
Environmental Health Perspectives  2014;123(4):367-373.
Background:
Perfluoroalkyl substances (PFASs) are persistent pollutants found to be endocrine disruptive and neurotoxic in animals. Positive correlations between PFASs and neurobehavioral problems in children were reported in cross-sectional data, but findings from prospective studies are limited.
Objectives:
We investigated whether prenatal exposure to PFASs is associated with attention deficit/hyperactivity disorder (ADHD) or childhood autism in children.
Methods:
Among 83,389 mother–child pairs enrolled in the Danish National Birth Cohort during 1996–2002, we identified 890 ADHD cases and 301 childhood autism cases from the Danish National Hospital Registry and the Danish Psychiatric Central Registry. From this cohort, we randomly selected 220 cases each of ADHD and autism, and we also randomly selected 550 controls frequency matched by child’s sex. Sixteen PFASs were measured in maternal plasma collected in early or mid-pregnancy. We calculated risk ratios (RRs) using generalized linear models, taking into account sampling weights.
Results:
Perfluorooctane sulfonate (PFOS) and perfluorooctanoic acid (PFOA) were detected in all samples; four other PFASs were quantified in ≥ 90% of the samples. We did not find consistent evidence of associations between mother’s PFAS plasma levels and ADHD [per natural log nanograms per milliliter increase: PFOS RR = 0.87 (95% CI: 0.74, 1.02); PFOA RR = 0.98 (95% CI: 0.82, 1.16)] or autism [per natural log nanograms per milliliter increase: PFOS RR = 0.92 (95% CI: 0.69, 1.22); PFOA RR = 0.98 (95% CI: 0.73, 1.31)]. We found positive as well as negative associations between higher PFAS quartiles and ADHD in models that simultaneously adjusted for all PFASs, but these estimates were imprecise.
Conclusions:
In this study we found no consistent evidence to suggest that prenatal PFAS exposure increases the risk of ADHD or childhood autism in children.
Citation:
Liew Z, Ritz B, von Ehrenstein OS, Bech BH, Nohr EA, Fei CY, Bossi R, Henriksen TB, Bonefeld-Jørgensen EC, Olsen J. 2015. Attention deficit/hyperactivity disorder and childhood autism in association with prenatal exposure to perfluoroalkyl substances: a nested case–control study in the Danish National Birth Cohort. Environ Health Perspect 123:367–373; http://dx.doi.org/10.1289/ehp.1408412
doi:10.1289/ehp.1408412
PMCID: PMC4383573  PMID: 25616253
9.  Paternal Age and Offspring Congenital Heart Defects: A National Cohort Study 
PLoS ONE  2015;10(3):e0121030.
Paternal age has been associated with offspring congenital heart defects (CHDs), which might be caused by increased mutations in the germ cell line because of cumulated cell replications. Empirical evidences, however, remain inconclusive. Furthermore, it is unknown whether all subtypes of CHDs are affected by paternal age. We aimed to explore the relationship between paternal age and the risk of offspring CHDs and its five common subtypes using national register data in Denmark. A total of 1 893 899 singletons born in Denmark from 1977 to 2008 were included in this national-based cohort study. Cox’s proportion hazards model with robust sandwich estimate option was used to estimate the hazards ratio (95% confidence interval) for the associations between paternal age and all CHDs, as well as subtypes of CHDs (patent ductus arteriosus (PDA), ventricular septal defect (VSD), atrial septal defect (ASD), tetralogy of fallot (TOF) and coarctation of the aorta (CoA)). We did not observe an overall association between paternal age and offspring CHDs. However, compared to the paternal age of 25–29 years, paternal age of older than 45 years was associated with a 69% increased risk of PDA (HR45+ = 1.69, 95%CI:1.17–2.43). We observed similar results when subanalyses were restricted to children born to mothers of 27–30 years old. After taking into consideration of maternal age, our data suggested that advanced paternal age was associated with an increased prevalence of one subtype of offspring congenital heart defects (CHDs), namely patent ductus arteriosus (PDA).
doi:10.1371/journal.pone.0121030
PMCID: PMC4373953  PMID: 25806788
10.  Spontaneous Abortion, Stillbirth and Hyperthyroidism: A Danish Population-Based Study 
European Thyroid Journal  2014;3(3):164-172.
Objectives
Pregnancy loss in women suffering from hyperthyroidism has been described in case reports, but the risk of pregnancy loss caused by maternal hyperthyroidism in a population is unknown. We aimed to evaluate the association between maternal hyperthyroidism and pregnancy loss in a population-based cohort study.
Study Design
All pregnancies in Denmark from 1997 to 2008 leading to hospital visits (n = 1,062,862) were identified in nationwide registers together with information on maternal hyperthyroidism for up to 2 years after the pregnancy [hospital diagnosis/prescription of antithyroid drug (ATD)]. The Cox proportional hazards model was used to estimate adjusted hazard ratio (aHR) with 95% confidence interval (CI) for spontaneous abortion (gestational age <22 weeks) and stillbirth (≥22 weeks), reference: no maternal thyroid dysfunction.
Results
When maternal hyperthyroidism was diagnosed before/during the pregnancy (n = 5,229), spontaneous abortion occurred more often both in women treated before the pregnancy alone [aHR 1.28 (95% CI 1.18-1.40)] and in women treated with ATD in early pregnancy [1.18 (1.07-1.31)]. When maternal hyperthyroidism was diagnosed and treated for the first time in the 2-year period after the pregnancy (n = 2,361), there was a high risk that the pregnancy under study had terminated with a stillbirth [2.12 (1.30-3.47)].
Conclusions
Both early (spontaneous abortion) and late (stillbirth) pregnancy loss were more common in women suffering from hyperthyroidism. Inadequately treated hyperthyroidism in early pregnancy may have been involved in spontaneous abortion, and undetected high maternal thyroid hormone levels present in late pregnancy may have attributed to an increased risk of stillbirth.
doi:10.1159/000365101
PMCID: PMC4224233  PMID: 25538898
Hyperthyroidism; Graves' disease; Antithyroid drug; Pregnancy; Pregnancy loss; Spontaneous abortion; Stillbirth
11.  Adverse pregnancy outcomes after exposure to methylphenidate or atomoxetine during pregnancy 
Clinical Epidemiology  2015;7:139-147.
Objective
To determine if prenatal exposure to methylphenidate (MPH) or atomoxetine (ATX) increases the risk of adverse pregnancy outcomes in women with attention deficit/hyperactivity disorder (ADHD).
Materials and methods
This was a population-based cohort study of all pregnancies in Denmark from 1997 to 2008. Information on use of ADHD medication, ADHD diagnosis, and pregnancy outcomes was obtained from nationwide registers.
Results
We identified 989,932 pregnancies, in which 186 (0.02%) women used MPH/ATX and 275 (0.03%) women had been diagnosed with ADHD but who did not take MPH/ATX. Our reference pregnancies had no exposure to MPH/ATX and no ADHD diagnosis. Exposure to MPH/ATX was associated with an increased risk of spontaneous abortion (SA; ie, death of an embryo or fetus in the first 22 weeks of gestation) (adjusted relative risk [aRR] 1.55, 95% confidence interval [CI] 1.03–2.36). The risk of SA was also increased in pregnancies where the mother had ADHD but did not use MPH/ATX (aRR 1.56, 95% CI 1.11–2.20). The aRR of Apgar scores <10 was increased among exposed women (aRR 2.06, 95% CI 1.11–3.82) but not among unexposed women with ADHD (aRR 0.99, 95% CI 0.48–2.05).
Conclusion
MPH/ATX was associated with a higher risk of SA, but our study indicated that it may at least partly be explained by confounding by indication. Treatment with MPH/ATX was however associated with low Apgar scores <10, an association not found among women with ADHD who did not use MPH/ATX.
doi:10.2147/CLEP.S72906
PMCID: PMC4317061  PMID: 25657597
attention deficit/hyperactivity disorder; ADHD; methylphenidate; atomoxetine; pregnancy outcomes
12.  Breast cancer risk after exposure to perfluorinated compounds in Danish women: a case–control study nested in the Danish National Birth Cohort 
Cancer Causes & Control  2014;25(11):1439-1448.
Objective
Animal studies have indicated that perfluoroalkylated substances (PFAS) increase mammary fibroadenomas. A recent case–control study in Greenlandic Inuit women showed an association between the PFAS serum levels and breast cancer (BC) risk. The present study evaluates the association between serum levels of PFAS in pregnant Danish women and the risk of premenopausal BC during a follow-up period of 10–15 years using prospectively collected exposure data during the pregnancy.
Methods
Questionnaire and blood samples were taken during 1996–2002 and at the end of follow-up, all 250 BC cases and 233 frequency-matched controls were chosen for further analyses. Serum levels of ten perfluorocarboxylated acids, five perfluorosulfonated acids, and one sulfonamide (perflurooctane-sulfonamide, PFOSA) were determined by liquid chromatography-tandem mass spectrometry with electrospray ionization in negative mode. Computer-assisted telephone interviews taken during pregnancy provided data on potential confounders.
Results
Weak positive and negative insignificant associations were found between BC risk and levels of perfluorooctane sulfonamide (PFOSA) and perfluorohexanesulfonate (PFHxS), respectively. Grouped into quintile, the BC cases had a significant positive association with PFOSA at the highest quintiles and a negatively association for PFHxS. Sensitivity analyses excluding uncertain cases caused stronger data for PFOSA and weaker for PFHxS. No further significant associations were observed.
Conclusions
This study does not provide convincing evidence for a causal link between PFAS exposures and premenopausal BC risks 10–15 years later.
Electronic supplementary material
The online version of this article (doi:10.1007/s10552-014-0446-7) contains supplementary material, which is available to authorized users.
doi:10.1007/s10552-014-0446-7
PMCID: PMC4215104  PMID: 25148915
Breast cancer; Perfluoroalkyl substances; Premenopausal Danish women; Prospective collected data
13.  Prenatal Exposure to Maternal Bereavement and Childbirths in the Offspring: A Population-Based Cohort Study 
PLoS ONE  2014;9(7):e103353.
Introduction
The decline in birth rates is a concern in public health. Fertility is partly determined before birth by the intrauterine environment and prenatal exposure to maternal stress could, through hormonal disturbance, play a role. There has been such evidence from animal studies but not from humans. We aimed to examine the association between prenatal stress due to maternal bereavement following the death of a relative and childbirths in the offspring.
Materials and Methods
This population-based cohort study included all subjects born in Denmark after 1968 and in Sweden after 1973 and follow-up started at the age of 12 years. Subjects were categorized as exposed if their mothers lost a close relative during pregnancy or the year before and unexposed otherwise. The main outcomes were age at first child and age-specific mean numbers of childbirths. Data was analyzed using Cox Proportional Hazards models stratified by gender and adjusted for several covariates. Subanalyses were performed considering the type of relative deceased and timing of bereavement.
Results
A total of 4,121,596 subjects were followed-up until up to 41 years of age. Of these subjects, 93,635 (2.3%) were exposed and 981,989 (23.8%) had at least one child during follow-up time. Compared to unexposed, the hazard ratio (HR) [95% confidence interval] of having at least one child for exposed males and females were 0.98 [0.96–1.01] and 1.01 [0.98–1.03], respectively. We found a slightly reduced probability of having children in females born to mothers who lost a parent with HR = 0.97 [0.94–0.99] and increased probability in females born to mothers who lost another child (HR = 1.09 [1.04–1.14]), the spouse (HR = 1.29 [1.12–1.48]) or a sibling (HR = 1.13 [1.01–1.27]).
Conclusions
Our results suggested no overall association between prenatal exposure to maternal stress and having a child in early adulthood but a longer time of follow-up is necessary in order to reach a firmer conclusion.
doi:10.1371/journal.pone.0103353
PMCID: PMC4113360  PMID: 25068458
14.  Mortality after Parental Death in Childhood: A Nationwide Cohort Study from Three Nordic Countries 
PLoS Medicine  2014;11(7):e1001679.
Jiong Li and colleagues examine mortality rates in children who lost a parent before 18 years old compared with those who did not using population-based data from Denmark, Sweden, and Finland.
Please see later in the article for the Editors' Summary
Background
Bereavement by spousal death and child death in adulthood has been shown to lead to an increased risk of mortality. Maternal death in infancy or parental death in early childhood may have an impact on mortality but evidence has been limited to short-term or selected causes of death. Little is known about long-term or cause-specific mortality after parental death in childhood.
Methods and Findings
This cohort study included all persons born in Denmark from 1968 to 2008 (n = 2,789,807) and in Sweden from 1973 to 2006 (n = 3,380,301), and a random sample of 89.3% of all born in Finland from 1987 to 2007 (n = 1,131,905). A total of 189,094 persons were included in the exposed cohort when they lost a parent before 18 years old. Log-linear Poisson regression was used to estimate mortality rate ratio (MRR). Parental death was associated with a 50% increased all-cause mortality (MRR = 1.50, 95% CI 1.43–1.58). The risks were increased for most specific cause groups and the highest MRRs were observed when the cause of child death and the cause of parental death were in the same category. Parental unnatural death was associated with a higher mortality risk (MRR = 1.84, 95% CI 1.71–2.00) than parental natural death (MRR = 1.33, 95% CI 1.24–1.41). The magnitude of the associations varied according to type of death and age at bereavement over different follow-up periods. The main limitation of the study is the lack of data on post-bereavement information on the quality of the parent-child relationship, lifestyles, and common physical environment.
Conclusions
Parental death in childhood or adolescence is associated with increased all-cause mortality into early adulthood. Since an increased mortality reflects both genetic susceptibility and long-term impacts of parental death on health and social well-being, our findings have implications in clinical responses and public health strategies.
Please see later in the article for the Editors' Summary
Editors' Summary
Background
When someone close dies, it is normal to grieve, to mourn the loss of that individual. Initially, people who have lost a loved one often feel numb and disorientated and find it hard to grasp what has happened. Later, people may feel angry or guilty, and may be overwhelmed by feelings of sadness and despair. They may become depressed or anxious and may even feel suicidal. People who are grieving can also have physical reactions to their loss such as sleep problems, changes in appetite, and illness. How long bereavement—the period of grief and mourning after a death—lasts and how badly it affects an individual depends on the relationship between the individual and the deceased person, on whether the death was expected, and on how much support the mourner receives from relatives, friends, and professionals.
Why Was This Study Done?
The loss of a life-partner or of a child is associated with an increased risk of death (mortality), and there is also some evidence that the death of a parent during childhood leads to an increased mortality risk in the short term. However, little is known about the long-term impact on mortality of early parental loss or whether the impact varies with the type of death—a natural death from illness or an unnatural death from external causes such as an accident—or with the specific cause of death. A better understanding of the impact of early bereavement on mortality is needed to ensure that bereaved children receive appropriate health and social support after a parent's death. Here, the researchers undertake a nationwide cohort study in three Nordic countries to investigate long-term and cause-specific mortality after parental death in childhood. A cohort study compares the occurrence of an event (here, death) in a group of individuals who have been exposed to a particular variable (here, early parental loss) with the occurrence of the same event in an unexposed cohort.
What Did the Researchers Do and Find?
The researchers obtained data on everyone born in Denmark from 1968 to 2008 and in Sweden from 1973 to 2006, and on most people born in Finland from 1987 to 2007 (more than 7 million individuals in total) from national registries. They identified 189,094 individuals who had lost a parent between the age of 6 months and 18 years. They then estimated the mortality rate ratio (MRR) associated with parental death during childhood or adolescence by comparing the number of deaths in this exposed cohort (after excluding children who died on the same day as a parent or shortly after from the same cause) and in the unexposed cohort. Compared with the unexposed cohort, the exposed cohort had 50% higher all-cause mortality (MRR = 1.50). The risk of mortality in the exposed cohort was increased for most major categories of cause of death but the highest MRRs were seen when the cause of death in children, adolescents, and young adults during follow-up and the cause of parental death were in the same category. Notably, parental unnatural death was associated with a higher mortality risk (MRR = 1.84) than parental natural death (MRR = 1.33). Finally, the exposed cohort had increased all-cause MRRs well into early adulthood irrespective of child age at parental death, and the magnitude of MRRs differed by child age at parental death and by type of death.
What Do These Findings Mean?
These findings show that in three high-income Nordic countries parental death during childhood and adolescence is associated with an increased risk of all-cause mortality into early adulthood, irrespective of sex and age at bereavement and after accounting for baseline characteristics such as socioeconomic status. Part of this association may be due to “confounding” factors—the people who lost a parent during childhood may have shared other unknown characteristics that increased their risk of death. Because the study was undertaken in high-income countries, these findings are unlikely to be the result of a lack of material or health care needs. Rather, the increased mortality among the exposed group reflects both genetic susceptibility and the long-term impacts of parental death on health and social well-being. Given that increased mortality probably only represents the tip of the iceberg of the adverse effects of early bereavement, these findings highlight the need to provide long-term health and social support to bereaved children.
Additional Information
Please access these websites via the online version of this summary at http://dx.doi.org/10.1371/journal.pmed.1001679.
The UK National Health Service Choices website provides information about bereavement, including personal stories; it also provides information about children and bereavement and about young people and bereavement, including links to not-for-profit organizations that support children through bereavement
The US National Cancer Institute has detailed information about dealing with bereavement for the public and for health professionals that includes a section on children and grief (in English and Spanish)
The US National Alliance for Grieving Children promotes awareness of the needs of children and teens grieving a death and provides education and resources for anyone who wants to support them
MedlinePlus provides links to other resources about bereavement (in English and Spanish)
doi:10.1371/journal.pmed.1001679
PMCID: PMC4106717  PMID: 25051501
15.  In utero exposure to alcohol and puberty in boys: a pregnancy cohort study 
BMJ Open  2014;4(6):e004467.
Objectives
Epidemiological studies have raised concerns about the reproductive consequences of in utero exposure to alcohol. Maternal lifestyle factors have been associated with altered pubertal development, but the impact of prenatal alcohol exposure on male puberty is unknown. Thus, the objective was to explore whether prenatal alcohol exposure alters pubertal development in boys.
Setting
Follow-up of a Danish pregnancy cohort.
Participants
Sons (N=2522) of women who were enrolled in a Danish pregnancy cohort between 1984 and 1987.
Primary and secondary outcome measures
Indicators of pubertal development, assessed by age at first nocturnal emission, voice break, acne and regular shaving.
Results
We found a tendency towards a later age at first nocturnal emission and voice break following in utero exposure to binge drinking. Boys exposed to ≥5 binge drinking episodes during pregnancy experienced their first nocturnal emission 7.3 months (95% CI −2.8 to 17.4) later and voice break 4.9 months (95% CI −0.6 to 10.4) later than the unexposed boys. Results for average weekly alcohol consumption were in the same direction, but differences were smaller and not statistically significant.
Conclusions
We found no strong support for the hypothesis that in utero exposure to weekly alcohol consumption is a risk factor for altered pubertal development, but a tendency towards delayed pubertal development among boys exposed to binge drinking during fetal life was observed. Longitudinal studies, with data collected as children go through puberty, are needed to explore this further.
doi:10.1136/bmjopen-2013-004467
PMCID: PMC4067820  PMID: 24916086
Epidemiology; Reproductive Medicine
16.  Psychiatric disorders following fetal death: a population-based cohort study 
BMJ Open  2014;4(6):e005187.
Objectives
Women have increased risks of severe mental disorders after childbirth and death of a child, but it remains unclear whether this association also applies to fetal loss and, if so, to which extent. We studied the risk of any inpatient or outpatient psychiatric treatment during the time period from 12 months before to 12 months after fetal death.
Design
Cohort study using Danish population-based registers.
Setting
Denmark.
Participants
A total of 1 112 831 women born in Denmark from 1960 to 1995 were included. In total, 87 687cases of fetal death (International Classification of Disease-10 codes for spontaneous abortion or stillbirth) were recorded between 1996 and 2010.
Primary and secondary outcome measures
The main outcome measures were incidence rate ratios (risk of first psychiatric inpatient or outpatient treatment).
Results
A total of 1379 women had at least one psychiatric episode during follow-up from the year before fetal death to the year after. Within the first few months after the loss, women had an increased risk of psychiatric contact, IRR: 1.51 (95% CI 1.15 to 1.99). In comparison, no increased risk of psychiatric contact was found for the period before fetal death. The risk of experiencing a psychiatric episode was highest for women with a loss occurring after 20 weeks of gestation (12 month probability: 1.95%, 95% CI 1.50 to 2.39).
Conclusions
Fetal death was associated with a transient increased risk of experiencing a first-time episode of a psychiatric disorder, primarily adjustment disorders. The risk of psychiatric episodes tended to increase with increasing gestational age at the time of the loss.
doi:10.1136/bmjopen-2014-005187
PMCID: PMC4054628  PMID: 24907247
Epidemiology; Obstetrics; Psychiatry
17.  Severe Maternal Stress Exposure Due to Bereavement before, during and after Pregnancy and Risk of Overweight and Obesity in Young Adult Men: A Danish National Cohort Study 
PLoS ONE  2014;9(5):e97490.
Background
Perinatal stress may programme overweight and obesity. We examined whether maternal pre- and post-natal bereavement was associated with overweight and obesity in young men.
Methods
A cohort study was conducted including 119,908 men born from 1976 to 1993 and examined for military service between 2006 and 2011. Among them, 4,813 conscripts were born to mothers bereaved by death of a close relative from 12 months preconception to birth of the child (exposed group). Median body mass index (BMI) and prevalence of overweight and obesity were estimated. Odds ratio of overweight (BMI≥25 kg/m2) and obesity (BMI≥30 kg/m2) were estimated by logistic regression analysis adjusted for maternal educational level.
Results
Median BMI was similar in the exposed and the unexposed group but the prevalence of overweight (33.3% versus 30.4%, p = 0.02) and obesity (9.8% versus 8.5%, p = 0.06) was higher in the exposed group. Conscripts exposed 6 to 0 months before conception and during pregnancy had a higher risk of overweight (odds ratio 1.15, 95% confidence interval (CI): 1.03; 1.27 and odds ratio 1.13, 95% CI: 1.03; 1.25, respectively). Conscripts born to mothers who experienced death of the child’s biological father before child birth had a two-fold risk of obesity (odds ratio 2.00, 95% CI: 0.93; 4.31). There was no elevated risk in those who experienced maternal bereavement postnatally.
Conclusion
Maternal bereavement during the prenatal period was associated with increased risk of overweight or obesity in a group of young male conscripts, and this may possibly be reflected to severe stress exposure early in life. However, not all associations were clear, and further studies are warranted.
doi:10.1371/journal.pone.0097490
PMCID: PMC4020839  PMID: 24828434
18.  Maternal Pre-Pregnancy BMI and Intelligence Quotient (IQ) in 5-Year-Old Children: A Cohort Based Study 
PLoS ONE  2014;9(4):e94498.
Background
An association between maternal pre-pregnancy BMI and childhood intelligence quotient (IQ) has repeatedly been found but it is unknown if this association is causal or due to confounding caused by genetic or social factors.
Methods
We used a cohort of 1,783 mothers and their 5-year-old children sampled from the Danish National Birth Cohort. The children participated between 2003 and 2008 in a neuropsychological assessment of cognitive ability including IQ tests taken by both the mother and the child. Linear regression analyses were used to estimate the associations between parental BMI and child IQ adjusted for a comprehensive set of potential confounders. Child IQ was assessed with the Wechsler Primary and Preschool Scales of Intelligence – Revised (WPPSI-R).
Results
The crude association between maternal BMI and child IQ showed that BMI was adversely associated with child IQ with a reduction in IQ of −0.40 point for each one unit increase in BMI. This association was attenuated after adjustment for social factors and maternal IQ to a value of −0.27 (−0.50 to −0.03). After mutual adjustment for the father's BMI and all other factors except maternal IQ, the association between paternal BMI and child IQ yielded a regression coefficient of −0.26 (−0.59 to 0.07), which was comparable to that seen for maternal BMI (−0.20 (−0.44 to 0.04)).
Conclusion
Although maternal pre-pregnancy BMI was inversely associated with the IQ of her child, the similar association with paternal BMI suggests that it is not a specific pregnancy related adiposity effect.
doi:10.1371/journal.pone.0094498
PMCID: PMC3984139  PMID: 24727836
19.  Birth weight, gestational age, fetal growth and childhood asthma hospitalization 
Background
Childhood asthma may have a fetal origin through fetal growth and development of the immunocompetence or respiratory organs.
Objective
We examined to which extent short gestational age, low birth weight and fetal growth restriction were associated with an increased risk of asthma hospitalization in childhood.
Methods
We undertook a cohort study based on several national registers in Denmark, Sweden and Finland. We included all live singleton born children in Denmark during 1979-2005 (N = 1,538,093), in Sweden during 1973-2004 (N = 3,067,670), and a 90% random sample of singleton children born in Finland during 1987-2004 (N = 1,050,744). The children were followed from three years of age to first hospitalization for asthma, emigration, death, their 18th birthday, or the end of study (the end of 2008 in Denmark, and the end of 2007 in Sweden or Finland), whichever came first. We computed the pseudo-values for each observation and used them in a generalized estimating equation to estimate relative risks (RR) for asthma hospitalization.
Results
A total of 131,783 children were hospitalized for asthma during follow-up. The risk for asthma hospitalization consistently increased with lower birth weight and shorter gestational age. A 1000-g decrease in birth weight corresponded to a RR of 1.17 (95% confidence interval (CI) 1.15-1.18). A one-week decrease in gestational age corresponded to a RR of 1.05 (95% CI 1.04-1.06). Small for gestational age was associated with an increased risk of asthma hospitalization in term but not in preterm born children.
Conclusions
Fetal growth and gestational age may play a direct or indirect causal role in the development of childhood asthma.
doi:10.1186/1710-1492-10-13
PMCID: PMC3973844  PMID: 24602245
Asthma; Birth weight; Gestational age; Hospitalization; Small for gestational age
20.  In-Utero Exposure to Bereavement and Offspring IQ: A Danish National Cohort Study 
PLoS ONE  2014;9(2):e88477.
Background
Intelligence is a life-long trait that has strong influences on lifestyle, adult morbidity and life expectancy. Hence, lower cognitive abilities are therefore of public health interest. Our primary aim was to examine if prenatal bereavement measured as exposure to death of a close family member is associated with the intelligence quotient (IQ) scores at 18-years of age of adult Danish males completing a military cognitive screening examination.
Methods
We extracted records for the Danish military screening test and found kinship links with biological parents, siblings, and maternal grandparents using the Danish Civil Registration System (N = 167,900). The prenatal exposure period was defined as 12 months before conception until birth of the child. We categorized children as exposed in utero to severe stress (bereavement) during prenatal life if their mothers lost an elder child, husband, parent or sibling during the prenatal period; the remaining children were included in the unexposed cohort. Mean score estimates were adjusted for maternal and paternal age at birth, residence, income, maternal education, gestational age at birth and birth weight.
Results
When exposure was due to death of a father the offsprings' mean IQ scores were lower among men completing the military recruitment exam compared to their unexposed counterparts, adjusted difference of 6.5 standard IQ points (p-value = 0.01). We did not observe a clinically significant association between exposure to prenatal maternal bereavement caused by death of a sibling, maternal uncle/aunt or maternal grandparent even after stratifying deaths only due to traumatic events.
Conclusion
We found maternal bereavement to be adversely associated with IQ in male offspring, which could be related to prenatal stress exposure though more likely is due to changes in family conditions after death of the father. This finding supports other literature on maternal adversity during fetal life and cognitive development in the offspring.
doi:10.1371/journal.pone.0088477
PMCID: PMC3928249  PMID: 24558394
21.  Epidemiologic methods for investigating male fecundity 
Asian Journal of Andrology  2013;16(1):17-22.
Fertility is a couple concept that has been measured since the beginning of demography, and male fecundity (his biological capacity to reproduce) is a component of the fertility rate. Unfortunately, we have no way of measuring the male component directly, although several indirect markers can be used. Population registers can be used to monitor the proportion of childless couples, couples who receive donor semen, trends in dizygotic twinning, and infertility diagnoses. Studies using time-to-pregnancy (TTP) may identify couple subfecundity, and TTP data will correlate with sperm quality and quantity as well as sexual activity and a number of other conditions. Having exposure data available for couples with a fecund female partner would make TTP studies of interest in identifying exposures that may affect male fecundity. Biological indicators such as sperm quality and quantity isolate the male component of fertility, and semen data therefore remain an important source of information for research. Unfortunately, often over half of those invited to provide a sperm sample will refuse, and the study is then subject to a selection that may introduce bias. Because the most important time windows for exposures that impair semen production could be early fetal life, puberty, and the time of ejaculation; longitudinal data over decades of time are required. The ongoing monitoring of semen quality and quantity should continue, and surveys monitoring fertility and waiting TTP should also be designed.
doi:10.4103/1008-682X.122198
PMCID: PMC3901876  PMID: 24369129
data collection; epidemiology; epidemiological monitoring; fertility; sperm count; time-to-pregnancy (TTP)
22.  Low Birth Weight in Children Born to Mothers with Hyperthyroidism and High Birth Weight in Hypothyroidism, whereas Preterm Birth Is Common in Both Conditions: A Danish National Hospital Register Study 
European Thyroid Journal  2013;2(2):135-144.
Objectives
Maternal hyper- and hypothyroidism have been associated with increased risk of adverse pregnancy outcomes, but studies have led to inconsistent results. We aimed to identify children born to mothers with a hospital-recorded diagnosis of thyroid dysfunction in Denmark and to study the association with gestational age at delivery and birth weight of the child.
Study Design
Population-based cohort study using Danish nationwide registers. All singleton live births in Denmark between January 1, 1978 and December 31, 2006 were identified and stratified by maternal diagnosis of hyper- or hypothyroidism registered in the Danish National Hospital Register before January 1, 2007.
Results
Maternal first-time diagnosis of thyroid dysfunction before, during or after pregnancy was registered in 32,809 (2.0%) of the singleton live births (n = 1,638,338). Maternal diagnosis of hyperthyroidism (adjusted OR 1.22, 95% CI 1.15-1.30) and hypothyroidism (adjusted OR 1.17, 95% CI 1.08-1.27) were associated with increased risk of preterm birth. Moreover, birth weight in children born to mothers with a diagnosis of hyperthyroidism was lower (adjusted difference −51 g, 95% CI −58 to −43 g) and higher in relation to maternal hypothyroidism (adjusted difference 20 g, 95% CI 10-30 g). Hyperthyroidism was associated with small-for-gestational-age (adjusted OR 1.15, 95% CI 1.10-1.20) and hypothyroidism with large-for-gestational-age children (adjusted OR 1.24, 95% CI 1.17-1.31).
Conclusions
Based on Danish nationwide registers, both maternal hyper- and hypothyroidism were associated with increased risk of preterm birth. Actual birth weight of the child and birth weight for gestational age were low if the mother had a diagnosis of hyperthyroidism and high if the diagnosis was hypothyroidism.
doi:10.1159/000350513
PMCID: PMC3821508  PMID: 24783052
Thyroid disease; Hyperthyroidism; Hypothyroidism; Iodine; Pregnancy; Gestational age; Birth weight; Birth length; Danish National Hospital Register

23.  Congenital Cerebral Palsy, Child Sex and Parent Cardiovascular Risk 
PLoS ONE  2013;8(11):e79071.
Objective
Genes associated with cardiovascular disease may also be risk factors for congenital cerebral palsy (CP) and these associations may be modified by sex, since there is an increased risk of CP in male children. We investigated the association between CP of the child with cardiovascular disease in parents, taking sex of the child into consideration.
Methods
All parents of non-adopted singletons born in Denmark between 1973 and 2003 were included. Parents of a child with CP, confirmed by the Danish National CP registry, were considered exposed. Cox proportional hazards regressions were used to model risk of cardiovascular outcomes for exposed parents compared to all other parents beginning at the child’s 10th birthday.
Results
We identified 733,730 mothers and 666,652 fathers among whom 1,592 and 1,484, respectively, had a child with CP. The mean age for mothers at end of follow up was 50±8 years. After adjustment for maternal age, parental education, child’s sex, child’s residence, child being small for gestational age and maternal hypertensive disorder during pregnancy, mothers of CP male children had an excess risk of cardiovascular disease (HR: 1.52, 95% CI: 1.16-2.00), attributable mostly to an increased incidence of hypertension and cerebrovascular disease. After additional adjustment for preterm birth, the association was markedly attenuated for cardiovascular disease (1.34, 95%CI: 1.02 - 1.76), became nonsignificant for hypertension, but remained significant for cerebrovascular disease (HR: 2.73, 95% CI: 1.45- 5.12). There was no increased risk of cardiovascular events in mothers of female CP children, or fathers of CP children of any sex.
Conclusions
Women that have a male child with CP are at increased risk for premature cardiovascular disease. Part of this association may be related to risk factors for preterm births.
doi:10.1371/journal.pone.0079071
PMCID: PMC3815096  PMID: 24223882
24.  Psychological Stress and Hospitalization for Childhood Asthma-a Nationwide Cohort Study in Two Nordic Countries 
PLoS ONE  2013;8(10):e78816.
Objective
Exposures to psychological stress in early life may contribute to the development or exacerbation of asthma. We undertook a cohort study based on data from several population-based registers in Denmark and Sweden to examine whether bereavement in childhood led to increased asthma hospitalization.
Methods
All singleton children born in Denmark during 1977-2008 and in Sweden during 1973-2006 were included in the study (N=5,202,576). The children were followed from birth to the date of first asthma hospitalization, emigration, death, their 18th birthday, or the end of study (31 December 2007 in Sweden and 31 December 2008 in Denmark), whichever came first. All the children were assigned to the non-bereaved group until they lost a close relative (mother, father or a sibling), from when they were included in the bereaved group. We evaluated the hazard ratio (HR) of first hospitalization for asthma in bereaved children using Cox proportional hazards regression models, compared to those who were in the non-bereaved group. We also did a sub-analysis on the association between bereavement and first asthma medication.
Results
A total of 147,829 children were hospitalized for asthma. The overall adjusted HR of asthma hospitalization in bereaved children was 1.10 (95% confidence interval (CI): 1.04-1.16), compared to non-bereaved children. The risk of asthma hospitalization was increased in those who lost a close relative at age of 14-17 years (HR=1.54, 95% CI: 1.23-1.92), but not in younger age groups. The association between bereavement and asthma hospitalization did not change over time since bereavement. In the sub-analysis in singleton live births during 1996-2008 recorded in the DMBR, bereavement was associated with a lower use of asthma medication (HR=0.87, 95% CI: 0.80-0.95).
Conclusions
Our data suggests that psychological stress following bereavement in late adolescence is associated with an increased risk of asthma hospitalization or lowers the threshold for asthma hospitalization.
doi:10.1371/journal.pone.0078816
PMCID: PMC3808299  PMID: 24205324
25.  Prenatal Antidepressant Exposure and Risk of Spontaneous Abortion – A Population-Based Study 
PLoS ONE  2013;8(8):e72095.
Purpose
To estimate the risk of spontaneous abortion after use of antidepressant medication during pregnancy.
Methods
From the Danish Medical Birth Registry and the Danish National Hospital Registry, we identified all pregnancies leading to in- or outpatient contacts in Denmark from February 1997 to December 2008. The Danish Registry of Medicinal Product Statistics provided information on the women's prescriptions for antidepressants during pregnancy. We obtained information on women who were diagnosed with depression from the Danish Psychiatric Central Registry. Adjusted relative risks (aRR) of spontaneous abortion were estimated according to exposure to antidepressants or maternal depression using binomial regression.
Results
Of the 1,005,319 pregnancies (547,300 women) identified, 114,721 (11.4%) ended in a spontaneous abortion. We identified 22,061 pregnancies exposed to antidepressants and 1,843 with a diagnosis of depression with no antidepressant use, of which 2,637 (12.0%) and 205 (11.1%) ended in a spontaneous abortion, respectively. Antidepressant exposure was associated with an aRR of 1.14 (95% confidence interval (CI) 1.10–1.18) for spontaneous abortion compared with no exposure to antidepressants. Among women with a diagnosis of depression, the aRR for spontaneous abortion after any antidepressant exposure was 1.00 (95% CI 0.80–1.24). No individual selective serotonin reuptake inhibitor (SSRI) was associated with spontaneous abortions. In unadjusted analyses, we found that mirtazapine, venlafaxine, and duloxetine were associated with spontaneous abortions among women with depression but we had no information on potential differences in disease severity and only few pregnancies were exposed in the population.
Conclusion
We identified a slightly increased risk of spontaneous abortion associated with the use of antidepressants during pregnancy. However, among women with a diagnosis of depression, antidepressants in general or individual SSRI in particular were not associated with spontaneous abortions. Further studies are warranted on the newer non-SSRI antidepressants, as we had insufficient data to adjust for important confounding factors.
doi:10.1371/journal.pone.0072095
PMCID: PMC3756033  PMID: 24015208

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