| Background. Previous studies suggest that elevated exposure to disinfection byproducts (DBPs) may lead to fetal growth restriction. The association between DBP exposure and preterm birth is unclear. This study examined the effects of trihalomethane (THM), haloacetic acid (HAA), and total organic halide (TOX) exposure on the probability of delivering a small-for-gestational age (SGA) infant, mean birth weight and preterm birth. Methods. Women were enrolled early in pregnancy (&le 12 week's gestation) or while planning a pregnancy from three U.S. communities from 2000-2004. Weekly (or biweekly) water samples were collected and analyzed for DBPs. Participant data were collected through interviews, an early ultrasound and birth records. Associations with total THM (TTHM), the sum of five HAAs (HAA5), and TOX were assessed using log-binomial regression for SGA (n=1,958) and preterm birth (n=2,039) and linear regression for term birth weight (n=1,854). A Bayesian analysis was conducted to examine associations between individual DBPs and fetal growth. Discrete-time hazard analysis was used to model the conditional odds of delivery each week in relation to DBPs. Results. HAA5 and TOX were not consistently associated with SGA or term birth weight. The risk ratio (95% confidence interval) associated with an average third trimester TTHM concentration above the regulatory standard (&ge 80 micrograms/liter) was 2.0 (1.1, 3.6). Results of the Bayesian model did not support a consistent association between any particular DBP and fetal growth. Conversely, average second trimester DBP levels were inversely associated with preterm birth: adjusted risk ratios (95% confidence interval) for preterm birth were 0.8 (0.5, 1.3), 0.9 (0.6, 1.4), 0.7 (0.4, 1.1) and 0.5 (0.3, 0.9) for increasing TTHM concentrations and 1.1 (0.8, 1.7), 0.8 (0.5, 1.2), 0.5 (0.3 0.8), and 0.7 (0.4, 1.1) for increasing HAA concentrations. The conditional odds of delivery each week also were decreased with elevated TTHM and HAA5 exposure for gestational weeks' 33-40. Conclusions. Results do not suggest an adverse effect of HAA or TOX exposure on fetal growth or an association with TTHM at average residential concentrations below the regulatory standard. In addition, results clearly indicate the probability of preterm birth is not increased with elevated DBP exposure. |
