The main feature and strength of the MISA study is the wide range of biological specimens collected from mothers during pregnancy, just after delivery, and 6 weeks postpartum; and from the newborns at birth. This is supplemented by the construction of a database that also includes maternal food-frequency questionnaire information and sociodemographic characteristics, as well as clinical information for both the mother and child. Once the available data is fully analyzed, the understanding gained should enhance our knowledge of the interplay between maternal diet, the physiological changes that occur in mothers during pregnancy and postpartum, and contaminant pharmacokinetics (including transfer to the infant before and after birth).
The average total energy intake by the study cohort was 8.1 MJ/day (median 8.1; range 3.1–16.4) with an average fish intake of 80 g/day (median 72 g/day; range 0–252 g/day), including 11.5 g/day (median 9 g/day, range 0–66 g/day) of fatty fish and 19.8 g/day (median 15.8 g/day, range 0–136 g/day) of lean fish (Table S1). One woman reported not to consume fish or fish products. For the study cohort and dropouts, the daily total average energy intake was below the Nordic Nutritional Recommendations (NNR) (18
): 73% were below 9.3 MJ, which is the recommended intake for women in the age group 18–60 with an average physical stature. Women with normal weight are recommended to increase their intake by 2.1 MJ during the first trimester, or 10.3–10.5 MJ per day. The average intakes reported here are also lower than that observed (mean of 9.8 MJ; 1999–2007 study period) in the Norwegian Mother and Child Cohort (MoBa) Study (19
). It is to be noted that the FFQ in the present study probed fish consumption in greater detail than its NOWAC parent did, but was nevertheless considerably shorter than the FFQ employed in the MoBa study (5 vs. 14 pages) (20
). However, nutrient intake per MJ (i.e. nutrient density) was in good compliance with NNR recommendations (18
) and a more recent Danish report (21
). Daily dietary intake among Norwegian and Sami women was comparable for most food items (22
Generally speaking, fish consumption has declined over the last decades. In a 1980 Norwegian study, 2.6% of the women aged 20–49 reported intakes of fish dinners 5–7 times a week (23
), compared to 0.5% by mothers in the MISA study. It is worth mentioning that during childhood, 8.9% reported fish intake 4 times or more per week. Young women are reported to consume less fish compared to the general public average (24
). Average total fish consumption in the MISA group was more than double that reported in the MoBa cohort (n=62,099, for the period 2002–2008), namely 80 g/day vs. 36 g/day (or 42 g/day for a subgroup of 119 who participated in the validation of the MoBa food frequency questionnaire) (24
). However seafood intake is indeed reported to be higher in Northern Norway compared to the rest of the country (26
). Our findings align well with those of another study performed above the Arctic Circle (27
); it reported annual fatty-fish consumption of 4200 g/year, compared to our assessment of 4138 g/year.
A comparison of the MBRN-registered data for the cohort subjects and the dropouts () indicated that there were no significant differences in gestational age at delivery, parity or induced delivery and mean birth weight of the newborns (although lower for the dropout mothers). The latter were also more likely to smoke, and this constitutes a rational explanation for lighter babies. Furthermore, compatibility extended to the consumption of most macronutrients and micronutrients, but somewhat lower intakes by the dropouts. In line with this, total energy intake was also lower (Table S1).
Average household income for families with children aged 0–5 in Norway in 2008 was 601,000 NOK (28
), and this is reflected in the current study. It also concurs with the observed high (95%) married/cohabited status, as well as the average parity of 0.98 and advanced (bachelor level) education (see ).
Distribution of pre-pregnancy BMI in the study cohort is similar to what is generally found in Norway for women in their 30s (29
): 10.4% in the MISA study were obese (BMI > 30) vs. 13.2% in the general Norwegian female population, and 1.0% reported being underweight (BMI < 18.5) vs. 1.7%.
No woman had diagnosed hypertension prior to pregnancy, whereas 9.0% had elevated blood pressure (BP) at delivery. This is a little higher than reported previously in American women aged 18–39 (7.2%) (30
), although it should be emphasized that in the MISA study BP was measured when the women entered the delivery unit (at 3 days postpartum, the proportion with high BP had declined to 4.9%). Only 2% were diagnosed with pre-eclampsia. In Norway, the prevalence in first-time delivering women is 5.1%, and the crude risk is 2.5% in women with 1 previous delivery (31
). Two thirds of the cases in the present study also occurred among the nullipara.
Breast-feeding is common in Norway. A study by the Norwegian Directorate of Health and others showed that only 1% of newborns were never nourished with mother's milk, and 4 weeks postpartum a total of 95% were breastfed (82% exclusively so) (32
). Corresponding proportions were reported in the MoBa study, with 84.6% and 79.1% being fully breast-fed 1 and 2 months after delivery respectively (33
). We observed comparable proportions (). However, the proportion of any breastfeeding was somewhat higher in our study (98.0% at 7 weeks, data not shown) than in the MoBa study (96.6% at 1 month and 94.0% at 2 months). No data were available beyond this period, but mothers with previous deliveries reported exclusively breastfeeding their children for 6 months (38%), or 4 months (26%). Most of these continued breastfeeding independent of the number of previous deliveries with supplements for 6 months or longer (73%); 16% continued for at least 12 months.
The prevalence of smoking in the study cohort was lower than that reported in the 2009 national Norwegian statistics (34
): 11.5% compared to 19% at the beginning of pregnancy, and 4.1% vs. 8% at the end. In this national report, on average 85% gave information about smoking habits, whereas in the current study 88% did so at the onset of pregnancy and 78% at the end. Only 2% of our respondents failed to report on tobacco use in the FFQ, which is consistent with the data in the MBRN (beginning of pregnancy; κ=0.72, p < 0.001; 95% CI [0.61;0.83]). Underreporting about smoking is common (35
). Since in our study no information is available for 22% at the end of pregnancy, the actual prevalence might be higher. Nevertheless, the national numbers quoted probably constitute an upper value.
Smoking appears most dominant in the younger groups. Among those aged 25 or less 32.1% reported smoking at the beginning of pregnancy, 12.7% among those aged 26–30, and 5.3% among the oldest group (36 years or more). Again, this is consistent with the national Norwegian statistics (34
Even though only few women describe themselves as teetotallers, alcohol consumption during pregnancy was minimal. It was statistically independent of the reported smoking habits. In fact among the few who reported any intake of alcohol, the majority were non-smokers. Prior to conception, beer was the most common alcoholic drink among the younger age-groups (up to and around 30 years) and declined with age. By contrast, the proportion of women who reported intake of wine increased as they got older. Intake of other types of spirits was limited. Habitual drinking seems not to be an issue for the study cohort.
Strengths and limitations
Some operational bases for the reduced size of the study cohort were pointed out in the Results section. From the feedback received from the field workers and participants, another frequent reason was complications at delivery or postpartum. Others were that the business of the delivery units discouraged the mothers, as well as study tiredness. The latter reflects multiple requests to participate in other research projects that focus on the North. Based on the comparison of the MBRN registered data for the cohort subjects and the dropouts (), we conclude that this turn of events has introduced minimal bias.
Even though the project is comprehensive, detailed planning prior to its implementation, continuous follow-up, and minor punching errors all helped the internal validity. Several attempts to increase interest and awareness of the project were carried out, but recruitment remained sluggish and the final sample size was less than targeted. Therefore the study is likely less representative than planned, although the generally good comparisons with the MBRN observed is encouraging.
The annual number of deliveries in Northern Norway is around 5,500 and are distributed between 3 counties. In Finnmark County, all 3 delivering units are represented in the study cohort. In Troms County, 1 delivering unit was not included and it represented close to 20% of deliveries there. In Nordland County there are a total of 9 delivery units, but only 2 were included in the study cohort. However, the participating units represented almost half of the total number of deliveries. It should be mentioned that in Bodø (the largest unit and city in the county) recruitment was limited to 1 obstetrical unit. County participation rates varied somewhat. Comparisons with averages for the all deliveries registered in the MBRN for the Northern Norway counties (live born, gestational age 30–42, n=15,571) for 2004–2006 is helpful. The women in the MISA cohort were on average 1–2 years older, and smoke less. However, many parameters were of comparable magnitude between the Northern Norway 2004–2006 mothers and the MISA group: mean birth weight (3,557 vs. 3,623 g) and the Apgar score at 5 minutes were the same (9.5); Apgar score% <7 at 5 minutes (1.2 vs. 1.3 for the MISA group); gestational age (39.3 vs. 39.6); parity (1.02 vs. 0.98); haemorrhage >1500 mL (0.9% vs. 0.8%); and polyhydramnion (1.3% vs. 1.3%).
The fact that the MISA cohort women were somewhat older and perhaps better schooled than the dropouts might well explain the lower smoking rate. Food consumption might also have been more selective in terms of healthy food choices. Not surprisingly, fish intake did not vary substantially between cohort members and dropouts, and this agrees well with the consumption of most micronutrients and macronutrients. Although the parent NOWAC FFQ has been validated, this did not involve pregnant women. This reduces the confidence in our findings somewhat. However, as indicated earlier, the consumption data obtained do align with other studies.
To date, studies of changes in the maternal concentrations during pregnancy and postpartum of organochlorines and of toxic and essential elements have been initiated (22
). The observed trends were interpreted in the context of underlying metabolic, haematological and physiological changes that occur in mothers. The MISA database also offers opportunities to explore the interplay of the physiological changes that occur in mothers with contaminant pharmacokinetics, including transfer to the infant before and after birth. Future investigations will also focus on associations between diet and contaminant levels for both the women and their offspring, and prospective studies are contemplated for exploring prenatal exposure and the developmental health of the children.