Blood lead concentrations and pregnancy outcomes.

LEAD is of the more extensively studied reproductive toxicants. (1) Lead readily crosses the placenta; therefore, it may cause fetal and maternal adverse outcomes, including low birth weight, preterm delivery, and congenital anomalies. (2-4) Lead concentrations have markedly declined in the last 2 decades because there have been concerted public health interventions; however, the potential for adverse maternal and fetal outcomes at lower blood lead concentrations remains unknown. (1,3,4) The identification of these risks requires multiple measurements of lead during pregnancy--a time when blood lead levels change. (5) A study of first trimester elective abortion tissues suggested that lead does not accumulate in the embryo/fetus during the first trimester; lead begins to cross the placenta during mid-pregnancy in animal models. (4) In the current study, we examined the relationship between adverse maternal events or newborn outcomes and low circulating blood lead concentrations in a nonselected population of women.

Materials and Method

The population comprised 705 enrollees who presented for prenatal care at 3 clinics that serve the Medicaid population in Camden, New Jersey. Ethnically, the study population, aged 12-34 yr, was 42% African American, 19% Caucasian, and 38% Hispanic, thus reflecting the racial and ethnic mix of the community. Exclusion criteria included a history of serious nonobstetric conditions (e.g., chronic hypertension, diabetes type I or II, drug or alcohol abuse, lupus, malignancies, seizure disorders). All participants provided written informed consent consistent with the policies of the Institutional Review Boards at the University of Medicine and Dentistry of New Jersey and the University of Michigan.

Data and blood samples were collected during each trimester of pregnancy, at delivery, and at the first postpartum visit. In addition to physical assessment and phlebotomy, each participant was interviewed at these times to determine her sociodemographic characteristics and medical history.

Blood lead concentrations. Whole blood was collected by venipuncture into trace-metal-free, heparinized vacutainer[R] tubes (Becton Dickinson [Rutherford, New Jersey]). Samples were mixed on a blood rocker for 2 min and aliquoted into prerinsed cryovials for storage at-70[degrees]C until analysis. Lead concentrations were determined in accordance with the method of Miller et al. (6) at 283.3 nm, and a model Z3030 Zeeman background-corrected atomic absorption spectrophotometer (Perkin-Elmer [Norwalk, Connecticut]) was used. Each analytical run was accompanied by the analysis of "Reference Material for Whole Blood" lots #039 and #041 (Wadsworth Laboratory, State of New York Department of Health). These reference materials were analyzed at the beginning and end of each analytical run, which typically included 27 blood samples. The mean and standard error (SE) for certified lead concentrations were 7.1 [+ or -] 0.5 [micro]g/dl and 3.6 [+ or -] 0.2 [micro]g/dl for lots #39 and #041, respectively. Analysis of these reference materials during analytical runs for this and other studies resulted in mean lead concentrations of 6.98 [+ or -] 0.59 [micro]g/dl and 3.60 [+ or -] 0.21 [micro]g/dl at the beginning and 7.00 [+ or -] 0.57 [micro]g/dl and 3.56 [+ or -] 0.29 [micro]g/dl at the end of each run (n = 66-104). We assessed instrument drift, which was less than 1.5%, by determining the within-run mean for each control and the departure from the mean for each analytical result. Our laboratory participates in the Centers for Disease Control and Prevention's (CDC's) "Blood Lead Laboratory Reference System" program and obtains results within [+ or -] 2% of the CDC's target values.

Outcomes. Diagnoses of hypertension in pregnancy (HIP), preeclampsia, or toxemia were abstracted from medical records and were based on blood pressure cutoff points of 140 (systole) and 90 (diastole). Preterm delivery was defined as the occurrence of birth prior to 37 wk gestation, as determined by ultrasound. Small birth weight for gestational-age neonates (SGA) were distinguished from infants of normal size in…