<p><strong>BACKGROUND: </strong>As population lead levels decrease, the toxic effects of lead may be distributed to more sensitive populations, such as infants with poor fetal growth.</p>

<p><strong>OBJECTIVES: </strong>To determine the association of prenatal lead exposure and fetal growth; and to evaluate whether infants with poor fetal growth are more susceptible to lead toxicity than those with normal fetal growth.</p>

<p><strong>METHODS: </strong>We examined the association of second trimester maternal blood lead levels (BLL) with birthweight-for-gestational age (BWGA) z-score in 944 mother-infant participants of the PROGRESS cohort. We determined the association between maternal BLL and BWGA z-score by using both linear and quantile regression. We estimated odds ratios for small-for-gestational age (SGA) infants between maternal BLL quartiles using logistic regression. Maternal age, body mass index, socioeconomic status, parity, household smoking exposure, hemoglobin levels, and infant sex were included as confounders.</p>

<p><strong>RESULTS: </strong>While linear regression showed a negative association between maternal BLL and BWGA z-score (β=-0.06 z-score units per log BLL increase; 95% CI: -0.13, 0.003; P=0.06), quantile regression revealed larger magnitudes of this association in the &lt;30th percentiles of BWGA z-score (β range [-0.08, -0.13] z-score units per log BLL increase; all P values&lt;0.05). Mothers in the highest BLL quartile had an odds ratio of 1.62 (95% CI: 0.99-2.65) for having a SGA infant compared to the lowest BLL quartile.</p>

<p><strong>CONCLUSIONS: </strong>While both linear and quantile regression showed a negative association between prenatal lead exposure and birthweight, quantile regression revealed that smaller infants may represent a more susceptible subpopulation.</p>

<p>Acetaminophen is the only over-the-counter pain reliever that is not contraindicated during pregnancy, but recent studies have questioned whether acetaminophen is safe for the fetus, particularly the developing brain. This prospective birth cohort study probed the previously observed association between in utero exposure to acetaminophen and neurodevelopment by using concentrations of acetaminophen measured in meconium, which more objectively captures exposure of the fetus than maternal report. Exposure, measured by liquid chromatography coupled with tandem mass spectrometry, was categorized into non-detection, low detection, and high detection levels. At age six to eight years, children completed a set of subtests from the Wechsler Intelligence Scale for Children, 4th edition. Additionally this study examined potential effect modification by child sex on the association between acetaminophen exposure and neurodevelopment. In fully adjusted models, in utero exposure to acetaminophen was not statistically significantly associated with decreased scores on any of the examined subtests in all children combined (n = 118). The effect of in utero acetaminophen exposure on the Coding subtest was marginally significantly different among boys and girls, with girls performing significantly better on the task with higher levels of acetaminophen compared to girls with undetectable levels of exposure [βgirls, low = 2.83 (0.97, 4.70), βgirls, high = 1.95 (-0.03, 3.93), βboys, low = 0.02 (-1.78, 1.81), βboys, high = -0.39 (-2.09, 1.31), pinteraction = 0.06]. Effect modification by child sex was not observed on other subtests. These results do not support prior reports of adverse neurodevelopmental effects of in utero exposure to acetaminophen.</p>