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Stephen J. Rothenberg,^1,2 Samuel Karchmer,¹ Lourdes Schnaas,¹ Estela Perroni,¹ Francisco Zea,¹ and Julio Fernández Alba¹

¹National Institute of Perinatology, Mexico City, DF CP11000 Mexico
²Department of Anesthesiology, Charles R. Drew University of Medicine and Science, Los Angeles, CA 90059 USA

Abstract
The first step in modeling lead kinetics during pregnancy includes a description of sequential maternal blood lead (PbB) during pregnancy and the factors controlling it. We analyzed PbB of 105 women living in the Valley of Mexico from week 12 to week 36 of pregnancy and again at parturition. We also used data from all women contributing blood at any stage of pregnancy to determine antecedents of PbB. Pregnancies were uneventful, and offspring were normal. Although geometric mean PbB level averaged around 7.0 µg/dl (0.34 µmol/l) , with a range of 1.0-35.5 µg/dl throughout pregnancy, analysis of variance revealed a significant decrease in mean PbB from week 12 to week 20 (1.1 µg/dl) and various significant increases in mean PbB from week 20 to parturition (1.6 µg/dl) . Regression analyses confirmed the positive linear PbB trend from 20 weeks to parturition and additional contributions of dietary calcium, reproductive history, lifetime residence in Mexico City, coffee drinking, and use of indigenous lead-glazed pottery. Although decreasing hematocrit has been suggested to explain first-half pregnancy PbB decrease, the time course of hematocrit decrease in the present study did not match the sequential changes in PbB. While hemodilution and organ growth in the first half of pregnancy may account for much of the PbB decrease seen between 12 and 20 weeks, the remaining hemodilution and accelerated organ growth of the last half of pregnancy do not predict the trend toward increasing maternal PbB concentration from 20 weeks to delivery. Mobilization of bone lead, increased gut absorption, and increased retention of lead may explain part of the upward PbB trend in the second half of pregnancy. Reduction of lifetime lead exposure may be required to decrease risk of fetal exposure. Key words: blood lead, bone lead, caffeine, calcium, pregnancy. Environ Health Perspect 102:876-880 (1994)

http://ehpnet1.niehs.nih.gov/docs/1994/102-10/rothenberg.html

Address correspondence to S. Rothenberg, Department of Developmental Neurobiology, Research Tower, National Institute of Perinatology, Montes Urales 800, Lomas Virreyes, México, DF CP11000, México.

This work was supported in part by the Ministry of Health, Mexico ; the International Lead Zinc Research Organization ; the U.S. EPA ; Council of Consultants in Epidemiology of Mexico ; National Council of Science and Technology of Mexico ; Friedrich Ebert Stiftung, Frandon Enterprises, General Motors of Mexico, and a gift from an anonymous donor. We gratefully acknowledge the support of Velvl Shor Pinsker, Carlos Quesnel, Vicente Salinas, German Villa Juárez, Reyna Hernández, and the medical residents and nursing staffs of the Obstetrical and Pediatric Services. We especially acknowledge the service of the obstetrical patients who donated their time and interest. We thank Irving Pérez Guerrero, Leticia Mercado Torres, Sandra Martínez Medina, and Aurora Muñoz Jiménez. We are grateful for statistical advice provided by Peter Gartside and Paul Succop. We also thank Michael Rabinowitz, Irva Hertz-Picciotto, and Ellen O'Flaherty for reviewing earlier versions of the manuscript.

Received 15 March 1994 ; accepted 25 July 1994.