Guidelines for the Identification and Management of Lead Exposure

0.70-mm Hg increase in third-trimester systolic blood pressure, and a 0.54-mm Hg increase in third-trimesterdiastolic blood pressure.PreeclampsiaPreeclampsia, a pregnancy-specific disorder associated with increased maternal and perinatal morbidity andmortality, is defined as a) systolic blood pressure ≥140 mm Hg and/or diastolic blood pressure ≥90 mm Hgbeginning after the 20th week of gestation and b) proteinuria ≥300 mg per 24 hours. Preeclampsia is usuallyassociated with edema, hyperuricemia, and a fall in glomerular filtration rate. Blood lead levels have been associatedwith the risk for preeclampsia, although the evidence is less clear than for gestational hypertension.Dawson et al. (2000) observed significant differences between normotensive (N = 20) and hypertensive or preeclamptic(N = 19) pregnancies with respect to red blood cell lead content. They found maternal blood pressureto be directly proportional to RBC lead content; however, the selection criteria and study population inthis small group at increased risk are not well-defined, so selection bias and confounding cannot be ruled out.In the 2004 study by Vigeh et al. noted above, there were no significant differences in blood lead concentrationsamong hypertensive subjects with proteinuria (N = 30) and those without proteinuria (N = 25). In anotherstudy by Vigeh et al. (2006), among 396 postpartum women in Tehran, 31 with preeclampsia had significantlyhigher blood lead levels (mean 5.09 ± 2.01 µg/dL) compared to 365 normotensive controls (mean 4.82 ±2.22 µg/dL) and significantly higher umbilical cord blood lead levels (mean 4.30 ± 2.49 µg/dL compared to 3.5± 2.09 µg/dL) (Vigeh et al. 2006). A 13-fold increased risk for preeclampsia compared to normotensive controls(mean blood lead 3.52 ± 2.09 µg/dL) was observed for every log-unit increase (~3 µg/dL) in blood lead. The1987 study by Rabinowitz et al. of 3,851 women delivering in Boston found no association between blood leadlevel and risk for preeclampia (Rabinowitz et al. 1987).Summary of the Evidence: Effects on Maternal HypertensionGestational hypertension and preeclampsia have been associated with adverse maternal and perinatal outcomes.Lead exposure has been associated with increased risk for gestational hypertension but the magnitudeof the effect, the exposure level at which risk begins to increase, and whether risk is most associatedwith acute or cumulative exposure, remain uncertain. It is unclear whether lead-induced increases in bloodpressure during pregnancy lead to severe hypertension or preeclampsia. However, even mild gestationalhypertension can be expected to lead to increased maternal and fetal monitoring, medical interventions, andadditional health care costs. Also, causality is unclear since preexisting hypertension reduces renal function,which in turn could result in the retention of lead.IMPACT OF LEAD EXPOSURE ON PREGNANCY OUTCOMESSpontaneous AbortionThere is consistent evidence that the risk for spontaneous abortion is increased by maternal exposure to highlevels of lead. In her review of studies on the association between elevated blood lead levels and spontaneousabortion, Hertz-Picciotto (2000) includes a detailed summary of studies involving high blood lead levels, whichcome primarily from the literature on industrial exposures in Europe during the 19th century. Yet few studieshave addressed the risk for spontaneous abortion at lower levels of exposure. Of those studies that have addressedthis issue, most reports provide limited evidence to support an association between maternal bloodlead levels of 0 to 30 µg/dL and increased risk for spontaneous abortion (Laudanski et al. 1991; Lindbohm et al.1992; McMichael et al. 1986; Murphy et al. 1990; Tabacova and Balabaeva 1993). However, the lack of evidencefor an association at these low-to-moderate blood lead levels may be due to methodologic deficiencies inthese studies, such as small sample sizes, lack of control for confounding, problems in case ascertainment,and/or limitations in exposure assessment (Hertz-Piccioto 2000).8