Description of Sample
The demographic descriptors for nondiagnosed and drug/alcohol-diagnosed births are reported in . African Americans and White non-Hispanics are disproportionately represented in the drug/alcohol-diagnosed group. Similarly, Asians, White Hispanics, and other race/ethnic groups are under-represented in the drug/alcohol-diagnosed group relative to their proportions in the nondiagnosed group. However, 39% of all drug/alcohol-diagnosed births were to White non-Hispanics, with this group representing the largest proportion of drug/alcohol-diagnosed births. A higher proportion of drug/alcohol-diagnosed births were to mothers who had 12 years or less years of education. Mean maternal age was similar in both groups. Drug/alcohol-diagnosed births were more likely paid for by Medicaid.
Description of Demographic Characteristics for Births without Drug/Alcohol Diagnoses, for Those with Drug/Alcohol Diagnoses, and for All Births Combined
In further comparisons (not in table), a higher proportion of women delivering drug/alcohol-diagnosed infants had no prenatal care (14 vs 1%), or began prenatal care in the second (28 vs 17%) or third trimester (10 vs 4%); consequently, they also had fewer prenatal visits (7.2 vs 11.1, t = 164.09, p<0.01). The average length of gestation was similar with exposed infants having a mean gestation of approximately 8.9 months compared to 9.2 months for the nonexposed. In drug/alcohol-diagnosed births, there was a higher proportion of very low birth weight (defined as ≤ 1499 g; 4% vs 1%) and low birth weight (defined as 1500 to 2499 g; 20 vs 5%) infants. The mean birth weight for the nondiagnosed group was 3360 g (SD = 591.7) and for the diagnosed group, 2905 g (SD = 709.8).
Unadjusted and Stratified Mortality Rates
The unadjusted and stratified risk ratios comparing mortality outcomes between nondiagnosed births and drug/alcohol-diagnosed births appear in and . Neonatal and postneonatal death rates are calculated based on the rate per 1000 live births. The total number of deaths used in the calculations is also reported.
Unadjusted Relative Risk and Stratified RRs of Maternal and Fetal Death for Drug/Alcohol-Diagnosed Births Relative to Nondiagnosed Births
Unadjusted Relative Risk and Stratified RRs for Neonatal and Postneonatal Deaths for Drug/Alcohol-Diagnosed Births Relative to Nondiagnosed Births
As shown in the second row of , the unadjusted RR of maternal death is 2.7 times greater if drug/alcohol use is diagnosed. However, the RR of maternal death is different when stratified by potential confounding variables. The increased risk of maternal death is less among drug/alcohol users who smoke (RR = 2.2). The risk of maternal death is significantly greater for White Hispanics (RR = 3.4) and women aged 20 to 34 years (RR = 3.2) with a drug/alcohol diagnosis. However, the RR of maternal death is less for drug/alcohol-diagnosed births if African American (RR = 2.1), and White non-Hispanic (RR = 2.1), or if looking at when the trimester prenatal care began (ranging from RR = 1.8 for no prenatal care to RR = 2.2 for initiation of care in the second trimester). Although the RR of maternal death was significantly elevated for other ethnicity groups, the CI was wider because of the smaller number of deaths.
The unadjusted RR of fetal death is 30% higher (RR = 1.3) for births with a drug/alcohol diagnosis during pregnancy than for nondiagnosed births (). Stratifying by race/ethnicity, maternal age, tobacco use, trimester prenatal care began, and birth weight demonstrated confounding of the fetal mortality risk. There was an increased risk of fetal death among drug/alcohol-diagnosed births as maternal age increased (RR = 1.2, 1.6, 1.9, respectively), with late initiation of prenatal care (RR = 1.5) and among infants born with birth weights greater than 2500 g (RR = 1.7). The risk of fetal death was less for African Americans (RR = 0.7) and other ethnicities (RR = 0.7) who had a drug/alcohol diagnosis. Tobacco use and birth weight also produced lower risks of fetal death (RR = 0.7 for tobacco use, RR = 0.4 for low birth weight) for drug/alcohol-diagnosed births.
The unadjusted RR of neonatal death was 2.4 times higher among drug/alcohol diagnosed-births (). This relationship varied by race/ethnicity, maternal age, tobacco use, trimester prenatal care began, and birth weight group. An increased risk of neonatal death with drug/alcohol-diagnosed births, after stratifying, was noted for White non-Hispanics (RR = 2.5), and maternal age group 20 to 34 years (RR = 2.7).
The unadjusted RR of postneonatal death was 4.3 times greater among drug/alcohol-diagnosed births (). This relationship also varied by all stratified variables. The variables with an increased risk of postneonatal death for drug/alcohol-diagnosed births, once stratified, were for Other race/ethnicity (RR = 4.8), women aged 20 to 34 years (RR = 4.7), and ≥35 years (RR = 5.3), women who had not used tobacco during pregnancy (RR = 4.4), and women who began prenatal care in the first trimester (RR = 4.4).
Relationship between Drug Use and Mortality
Odd ratios were calculated to examine the relationship between drug use and mortality (). The odds of maternal death were significantly increased for all drug categories compared to no drug use during pregnancy. The odds of fetal death were significantly increased only for amphetamine use and polydrug use, whereas the odds of neonatal and postneonatal mortality were significantly increased for all drug categories.
ORs and 95% Confidence Limits from Logistic Regression Model of Mortality Predicted from Types of Drug Use Relative To No Drug Use
To assess whether drug/alcohol-diagnosed births were at higher risk for maternal, fetal, neonatal, and postneonatal mortality, given the results of the univariate analyses, four models were tested using multivariate logistic regression in order to adjust for potential confounding. Variables included in the models were not highly correlated (Pearson correlation coefficients ranging from r = 0.001 to 0.45). The highest correlations were between health insurance coverage and age, ethnicity/race, and educational level, therefore, health insurance coverage was not included in the analyses (see ).
OR and Wald 95% CI from Four Logistic Regressions Models Predicting Maternal, Fetal, Neonatal, and Postneonatal Death
In the first model, the odds of maternal death were doubled (odds ratio (OR) = 2.15) for women who used cocaine during pregnancy, by 92% for women who smoked tobacco, and three times more likely if women received no prenatal care, even after controlling for other factors. Race/ethnicity, maternal age group, and education level were not significant once all other factors were included in the model. In the second model, the odds of fetal death were significantly increased for women aged 35 years or greater (OR = 1.29), African American (OR = 1.12), White Hispanic (OR= 1.06), less than 12 years education (OR = 1.11), and no prenatal care (OR = 2.18), even after controlling for other variables. Low birth weight infants were 34 times more likely to have a fetal death (OR = 34.7), even after controlling for other factors. However, drug use, adolescents, other race/ethnicities, and tobacco use have a significant protective effect against fetal death, once controlled for other variables.
In the third model, only four variables significantly increased the odds of neonatal death, after controlling for all other variables: African American (OR = 1.16), less than 12 years education (OR = 1.13), no prenatal care (OR = 2.25), and low birth weight (OR = 48.3). Other ethnicities, cocaine, polydrug, and other drugs/alcohol were significant but had a protective effect. Maternal age group, White Hispanic ethnicity, amphetamine, and tobacco use were not significant. In the fourth model, the odds of postneonatal death were significantly increased for adolescents (OR = 1.33), African Americans (OR = 1.60), less than 12 years of education (OR = 1.40), tobacco use during pregnancy (OR = 1.80), no prenatal care (OR = 1.85), low birth weight (OR = 6.34), and for all drug categories, even after controlling for all factors. For women aged 35 years or greater (OR = 0.89) and White Hispanic women (OR = 0.81), there was a significant protective effect.