The determination of critical windows of susceptibility to environmental chemical exposures and health has become a major public health focus. This study examined the association between early age at exposure to
polybrominated biphenyls (PBBs) and subsequent
birth weight and gestational length in offspring among females. The study population consisted of 1111 births that occurred among 560 women enrolled in the Michigan PBB Cohort from 1975 to 1994. Maternal age at exposure was categorized into three groups:<10 years (n = 64), 11-16 years (n = 149), and 17-42 years (n = 347). Overall serum PBB levels ranged from 0 to 1490 ppb, with a median of 2, 3, and 2 ppb in the three age groups, respectively. Separate mixed-effects linear regression models were used to evaluate the effect of age at exposure (years) and initial PBB level (ppb) on
birth weight (grams) and gestational age (weeks), controlling for gestational age (weeks) (in the model examining effects on
birth weight), BMI (kg/m(2)) and serum PCB level at enrollment (ppb), maternal age and paternal education at delivery, parity, infant gender, interval between the initial serum test and date of delivery (years), and the trimester in which
prenatal care was initiated. Relative to the oldest age group, age<10 years at exposure was the most important predictor of increased
birth weight (estimated regression coefficient = 225 g, P = 0.012). Infant
birth weight increased approximately 16 g for every 10 ppb increase in serum PBBs (P=0.004). There was no association between initial PBB levels and gestational age, nor were initial serum PCB levels associated with either infant
birth weight or gestational length. These results provide support for the hypothesis that early age at exposure may be an important determinant in subsequent health effects due to environmental chemical exposures.