Blood lead levels measured prospectively and risk of spontaneous abortion

Studies of low to moderate level lead exposures have reported mixed findings regarding the risk of spontaneous abortion, despite lead's abortifacient properties at very high doses. To evaluate the risk of spontaneous abortion from low or moderate lead exposures, a nested case-control study was conducted within a cohort of pregnant women in Mexico City, 1994-1996. During their first trimester, 668 women enrolled, were interviewed, and contributed blood specimens. Pregnancies were followed by home visits or telephone calls. Spontaneous abortions before week 21 (n = 35) were matched with pregnancies that survived beyond week 20 (n = 60) on maternal age, hospital, date of enrollment, and gestational age at enrollment. Mean blood lead levels were 12.03 microg/dL for cases and 10.09 microg/dL for controls (p = 0.02). Odds ratios for spontaneous abortion comparing 5-9, 10-14, and > or =15 microg/dL with the referent category of <5 microg/dL of blood lead were 2.3, 5.4, and 12.2, respectively, demonstrating a significant trend (p = 0.03). After multivariate adjustment, the odds ratio for spontaneous abortion was 1.8 (95% confidence interval = 1.1, 3.1) for every 5 microg/dL increase in blood lead. Low to moderate lead exposures may increase the risk for spontaneous abortion at exposures comparable to US general population levels during the 1970s and to many populations worldwide today; these are far lower than exposures encountered in some occupations.