Air Pollution and Risk of Placental Abruption: A Study of Births in New York City, 2008-2014

Abstract

We evaluated the associations of exposure to fine particulate matter (particulate matter with an aerodynamic diameter ≤2.5 μm (PM2.5) at concentrations of <12 μg/m3, 12-14 μg/m3, and ≥15 μg/m3) and nitrogen dioxide (at concentrations of <26 parts per billion (ppb), 26-29 ppb, and ≥30 ppb) with placental abruption in a prospective cohort study of 685,908 pregnancies in New York, New York (2008-2014). In copollutant analyses, these associations were examined using distributed-lag nonlinear models based on Cox models. The prevalence of abruption was 0.9% (n = 6,025). Compared with a PM2.5 concentration less than 12 μg/m3, women exposed to PM2.5 levels of ≥15 μg/m3 in the third trimester had a higher rate of abruption (hazard ratio (HR) = 1.68, 95% confidence interval (CI): 1.41, 2.00). Compared with a nitrogen dioxide concentration less than 26 ppb, women exposed to nitrogen dioxide levels of 26-29 ppb (HR = 1.11, 95% CI: 1.02, 1.20) and ≥30 ppb (HR = 1.06, 95% CI: 0.96, 1.24) in the first trimester had higher rates of abruption. Compared with both PM2.5 and nitrogen dioxide levels less than the 95th percentile in the third trimester, rates of abruption were increased with both PM2.5 and nitrogen dioxide ≥95th percentile (HR = 1.44, 95% CI: 1.15, 1.80) and PM2.5 ≥95th percentile and nitrogen dioxide <95th percentile (HR = 1.43 95% CI: 1.23, 1.66). Increased levels of PM2.5 exposure in the third trimester and nitrogen dioxide exposure in the first trimester are associated with elevated rates of placental abruption, suggesting that these exposures may be important triggers of premature placental separation through different pathways.

Keywords: cohort studies; distributed-lag models; nitrogen dioxide; particulate matter; placental abruption.

Figure 1

Selection of the cohort for a study of air pollution and risk of placental abruption, New York, New York, 2008–2014. Data were derived from all births taking place in New York City (NYC) between December 2008 and December 2014 and linked to maternal and newborn hospitalizations. LMP, last menstrual period.

Figure 2

Association between exposure to particulate matter with an aerodynamic diameter ≤2.5 μm (PM_2.5) from 1 month before pregnancy to 10 months of pregnancy and rate of placental abruption, by month of delivery, New York, New York, 2008–2014. Adjusted hazard ratios were based on copollutant analysis adjusting for nitrogen dioxide exposure and confounders. A) Pregnancies lasting 10 months (n = 630,808); B) pregnancies lasting 9 months (n = 43,746); C) pregnancies lasting 8 months (n = 6,938); D) pregnancies lasting 7 months (n = 893). Distributed-lag nonlinear models based on marginal Cox proportional hazards regression were developed to account for repeat pregnancies in a given woman based on generalized estimating equations, where we allowed baseline abruption rates to differ according to maternal race/ethnicity and hospital at study entry. PM_2.5 exposure was modeled based on 3 degrees of freedom. Hazard ratios were adjusted for year of conception, season of conception, maternal age, maternal age squared, parity, education, smoking 3 months prior to conception or during pregnancy, prepregnancy body mass index (weight (kg)/height (m)²), body mass index squared, marital status, Medicaid enrollment, multiple births, percentage of households below the federal poverty level, percentage of households below the poverty level squared, median annual income, and median income squared.

Figure 3

Association between nitrogen dioxide exposure from 1 month before pregnancy to 10 months of pregnancy and rate of placental abruption, by month of delivery, New York, New York, 2008–2014. Adjusted hazard ratios (circles) and 95% confidence intervals (bars) for placental abruption were based on a 6–parts per billion increase in nitrogen dioxide exposure, derived from a copollutant analysis adjusting for PM_2.5 exposure and confounders. A) Pregnancies lasting 10 months (n = 630,808); B) pregnancies lasting 9 months (n = 43,746); C) pregnancies lasting 8 months (n = 6,938); D) pregnancies lasting 7 months (n = 893). Distributed-lag nonlinear models based on marginal Cox proportional hazards regression were developed to account for repeat pregnancies in a given woman based on generalized estimating equations, where we allowed baseline abruption rates to differ according to maternal race/ethnicity and hospital at study entry. Hazard ratios were adjusted for year of conception, season of conception, maternal age, maternal age squared, parity, education, smoking 3 months prior to conception or during pregnancy, prepregnancy body mass index (weight (kg)/height (m)²), body mass index squared, marital status, Medicaid enrollment, multiple births, percentage of households below the federal poverty level, percentage of households below the poverty level squared, median annual income, and median income squared.