Maternal blood lead

The effects of low levels of lead on birth weight and gestational age are controversial. The earlier evidence for such effects was not reproduced in more studies by Factor-Litvak et al. (1991) and Greene and Emhart (1991). A significant inverse association between prenatal maternal blood lead levels and birth weight was reported in the Cincinnati study (Bomschein et al. 1989 Dietrich et al. 1986, 1987a). 

Rothenberg SJ Charles R. Drew University of Medicine Science, Los Angeles, CA The role of prepregnancy maternal bone lead and prenatal maternal blood lead upon alterations in infant saccadic and smooth pursuit eye movements National Institute of General Medical Sciences... 

McMichael AJ, Vimpani GV, Robertson EF, et al. 1986. The Port Pirie cohort study Maternal blood lead and pregnancy outcome. J Epidemiol Community 40 18-25. 

Rothenberg SJ, Manalo M, Jiang J, et al. 1999a. Maternal blood lead level and blood pressure during pregnancy in South Central Los Angeles. Archives of Environmental Health, in press. 

High-dose lead exposure is a recognized risk factor for stillbirth or spontaneous abortion. Epidemiologic studies of the impact of low-level lead exposure on reproductive outcome such as low birth weight, preterm delivery, or spontaneous abortion have yielded mixed results. However, a well-designed nested case-control study recently detected an odds ratio for spontaneous abortion of 1.8 (95% Cl 1.1-3.1) for every 5 / g/dL increase in maternal blood lead across an approximate range of 5-20 g/dL (Boija-Aburto et al, 1999). In males, blood lead concentrations in excess of 40 / g/dL have been associated with diminished or aberrant sperm production. 

A special form of excretion of endogenous lead is through breast milk. Studies of breast milk indicate that lead concentrations correlate with maternal blood lead concentrations most studies reported that lead secreted from breast milk varies in concentration between 10 and 30% of maternal blood lead concentration (WHO, 1995). 

II. Maternal Blood Lead Levels During Pregnancy... 

Maternal blood lead levels and umbilical cord blood lead levels are the most direct measure of fetal exposure to lead, reflecting recent lead exposure and lead mobilized from tissue stores (Mushak 1989). Recent studies of mobilized... 

Mahaffey KR, Goyer R, Haseman JK (1973) Dose-response to lead ingestion in rats fed low dietary calcium. J Lab Clin Med 82 92-100 Manci EA, Blackburn WR (1987) Regional variations in the levels of zinc, iron, copper, and calcium in the term human placenta. Placenta 8 497-502 Markovac J, Goldstein GW (1988) Lead activates protein kinase C in immature rat brain microvessels. Toxicol Appl Pharmacol 96 14-23 McMichael AJ, Vimpani GV, Robertson EF, Baghurst PA, Clark PD (1986) The Port Pirie study maternal blood lead and pregnancy outcome. J Epidemiol Community Health 40 18-25... 

Moore, M.R., Goldberg, A., Meredith, P.A., Lees, R., Low, R.A. and Pocock, S.J. (1979). The contribution of drinking water lead to maternal blood lead concentrations, Clinica et Chimica Acta, 95, 129-133. 

Maternal blood lead measured at delivery (del) or at prenatal clinic visit (pre). 

The Cincinnati study also has found an effect of prenatal lead exposure on gestational age, measured in weeks as a continuous variable. One analysis (Dietrich et al, 1986) indicated that gestational age was reduced by approximately 0.6 week for each natural log unit of prenatal maternal blood lead (PbB measurements were transformed to natural logarithms for these analyses to better approximate a normal distribution). Also related to these findings is the cross-sectional study by Moore et al (1982), which has shown a significant relationship between pre-term delivery and either maternal or cord PbB levels in Glasgow, Scotland. This relationship held even after adjustment for a number of possible confounders. 

McMichael, A.J., Vimpani, G.V., Robertson, E.F., Baghurst, P.A. and Clark, P.D. (1986). The Port Pirie cohort study maternal blood lead and pregnancy outcome. ]. Epidemiol. Commun. Health, 40, 18-25... 

Recently, several large epidemiological studies have reported an association between low-level maternal blood lead (PbB) concentrations and various indices of adverse reproductive outcome, including preterm delivery (McMichael et al, 1986), low birth weight (Dietrich et al, in press), an increased incidence of minor anomalies (Needleman et al, 1984), and indices... 

This interim report has examined the potential impact of elevated maternal blood lead concentrations during pregnancy on indices of physical size at... 

Figure 1 The unadjusted relationship between maternal blood lead concentration and infant weight at birth n = 202 r = —0.18 p = <0.001...

Table 4 Multiple regression models for association between maternal blood lead and foetal size at birth n = 202)...

Figure 3 The estimated relationship between maternal blood lead concentration and birth weight after controlling for significant covariates and confounders. The significant (p < 0.008) blood lead by maternal age interaction is show n = 202...

The findings are also significant when one considers the level of lead exposure associated with this effect. Based on the recent National Health and Nutrition Examination Survey (Annest et al, 1982), 500 000 women of childbearing age have blood lead concentrations in excess of 12)Ugdl L Infants born to these women are more likely to weigh less and are therefore bom at higher risk for neurobehavioural delays, disorders and deficits than would be expected at maternal blood lead concentrations less than 6figdl. ... 

Evidence from several recent prospective and retrospective studies indicates that lead may be psychoteratogenic at relatively low levels of foetal exposure. In the present interim study, lead measured in whole blood during the prenatal (maternal blood lead) and neonatal periods was found to be inversely related to a complex of sensorimotor developmental indices at 6 and 12 months. Prenatal blood lead was also related to lower birth weight, which in turn was related to poorer sensorimotor performance in infants during the first year. These adverse effects were observed at levels of lead exposure common in pregnant women in the United States, Europe, and other developed areas. 

These analyses focused on four lead exposure variables prenatal (maternal) blood lead (PbBPre) as an index of prenatal exposure 10-day neonatal blood lead (PbBl) as another index of prenatal exposure and maximum first-year blood lead (MaxPbB) and cumulative 12-month blood lead (CumPbB) as indices of postnatal exposure. MaxPbB was the highest postnatal PbB value recorded for each infant at any assessment between 3 and 12 months of age. CumPbB was derived from calculation of the area under the curve of each child s PbB profile from 10 days to 12 months. This integrated index was used to characterize historical postnatal lead exposure in assessing developmental effects. 

This question has already been addressed under the previous heading. Higher prenatal (maternal) blood lead levels were associated with lower birth weight. As expected, birth weight continued to be positively related to Bayley MDI at 12 months. 

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