Fetal Lead Exposure: Timing Is Everything for Effects

Abstract

Vol. 114, No. 11 EnvironewsOpen AccessFetal Lead Exposure: Timing Is Everything for Effectsis accompanied byFetal Lead Exposure at Each Stage of Pregnancy as a Predictor of Infant Mental Development Carol Potera Carol Potera Search for more papers by this author Published:1 November 2006https://doi.org/10.1289/ehp.114-a661aAboutSectionsPDF ToolsDownload CitationsTrack Citations ShareShare onFacebookTwitterLinked InReddit Many countries have set guidelines for levels of environmental lead exposure that are considered safe for children. However, relatively few studies have focused exclusively on the role of prenatal lead exposure on infant neurodevelopment. Indeed, studies conducted in the past 20 years have shown inconsistent results, perhaps because of variability in when prenatal lead was measured (first, second, or third trimester) and in what type of sample (maternal plasma, maternal whole blood, or umbilical cord blood). A comprehensive study published this month is the first to compare such variables [EHP 114: 1730–1735; Hu et al.].From 1997 to 1999, the investigators measured lead levels of 146 pregnant women living in Mexico City. Leaded gasoline was sold in Mexico City until 1997, and bone lead levels in women there are about three times higher than in the United States. The leaching of lead stored in a mother’s bones provides a major source of fetal lead exposure.The investigators obtained samples of plasma and whole blood during each trimester and umbilical cord blood at delivery. They also tested the neurodevelopment of the children at age 24 months using the Mental Development Index (MDI), which evaluates memory, language, and sensory abilities.The authors found that lead exposure during the first trimester of pregnancy was more strongly linked to later decreases in the MDI scores than exposure during the latter two trimesters. Moreover, maternal plasma lead was the best predictor of a child’s later neurobehavioral performance because most of the lead in whole blood is attached to red cells and cannot cross the placenta. Each increase of 1 standard deviation unit in plasma lead lowered the MDI score by 3.5 points. Neither maternal levels in the second or third trimester nor cord blood levels impacted MDI scores in as strong a fashion.The results raise two questions: should lead be routinely measured in the first trimester of pregnancy, and are there ways to reduce fetal exposure? Plasma lead is expensive and difficult to measure, according to the authors, making routine clinical testing impractical. Studies suggest that calcium supplements slow the release of lead from bone. An ongoing clinical trial of pregnant women is assessing the efficacy of this intervention.Early threatA study of pregnant women in Mexico City showed that fetal lead exposure during the first trimester had a greater impact on later neurodevelopment than exposure in other trimesters.FiguresReferencesRelatedDetailsRelated articlesFetal Lead Exposure at Each Stage of Pregnancy as a Predictor of Infant Mental Development19 July 2006Environmental Health Perspectives Vol. 114, No. 11 November 2006Metrics About Article Metrics Publication History Originally published1 November 2006Published in print1 November 2006 Financial disclosuresPDF download License information EHP is an open-access journal published with support from the National Institute of Environmental Health Sciences, National Institutes of Health. All content is public domain unless otherwise noted. Note to readers with disabilities EHP strives to ensure that all journal content is accessible to all readers. However, some figures and Supplemental Material published in EHP articles may not conform to 508 standards due to the complexity of the information being presented. If you need assistance accessing journal content, please contact [email protected]. Our staff will work with you to assess and meet your accessibility needs within 3 working days.