Effect of magnitude and timing of maternal pregnancy blood lead (Pb) levels on birth outcomes.

OBJECTIVE: Associations between magnitude and timing of maternal pregnancy blood lead (Pb) levels (BLLs), birth weight, and total days of gestation were examined, as well as associations with related clinical diagnoses of low birth weight (LBW), preterm, and small-for-gestational-age (SGA) birth.

STUDY DESIGN: Among a sample of 262 mother-infant pairs studied retrospectively, one-way analysis of variance and regression statistics were used to measure the relationship between level of maternal pregnancy BLLs and birth outcomes while controlling for key maternal and newborn factors.

RESULTS: Women with maximum pregnancy BLLs (max-PBLLs) > or =10 microg/dl tended to give birth earlier and their babies were at substantially increased risk for preterm and SGA birth. By holding other explanatory factors constant, each unit increase in max-PBLL above 10 mug/dl was found to be associated with a decrease of -0.3 in total days of gestation. Compared to women with lower levels, women with max-PBLLs > or =10 microg/dl were at a threefold increased risk for preterm birth (adjusted OR=3.2, 95% CI 1.2-7.4) and more than a fourfold increased risk for having an SGA infant (adjusted OR=4.2, 1.3-13.9). Second trimester maximum BLLs > or =10 microg/dl were associated with a steep decrease in total days of gestation (a decrease of -1.0 days per each unit increase above 10 microg/dl).

CONCLUSIONS: These data provide evidence of the adverse effects of maternal pregnancy BLLs, particularly when levels are > or =10 microg/dl. Prenatal Pb exposure at these levels was associated with significant decreases in total days of gestation and an increased risk of preterm and SGA birth.