CHANGES IN SERIAL BLOOD LEAD LEVELS DURING PREGNANCY

The first step in modeling lead kinetics during pregnancy includes a d escription of sequential maternal blood lead (PbB) during pregnancy an d the factors controlling it. We analyzed PbB of 105 women living in t he 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 an y stage of pregnancy to determine antecedents of PbB. Pregnancies were uneventful, and offspring were normal. Although geometric mean PbB le vel averaged around 7.0 mu g/dl (0.34 mu mol/l), with a range of 1.0-3 5.5 mu g/dl throughout pregnancy, analysis of variance revealed a sign ificant decrease in mean PbB from week 12 to week 20 to (1.1 mu g/dl) and various significant increases in mean PbB from week 20 to parturit ion (1.6 mu g/dl). Regression analyses confirmed the positive linear P bB trend from 20 weeks to parturition and additional contributions of dietary calcium, reproductive history, lifetime residence in Mexico Ci ty, coffee drinking, and use of indigenous lead-glazed pottery. Althou gh decreasing hematocrit has been suggested to explain first-half preg nancy PbB decrease, the time course of hematocrit decrease in the pres ent study did not match the sequential changes in PbB. While hemodilut ion and organ growth in the first half of pregnancy may account for mu ch of the PbB decrease seen between 12 and 20 weeks, the remaining hem odilution and accelerated organ growth of the last half of pregnancy d o not predict the trend toward increasing maternal PbB concentration f rom 20 weeks to delivery. Mobilization of bone lead, increased gut abs orption, and increased retention of lead may explain part of the upwar d PbB trend in the second half of pregnancy. PbB trend in the second h alf of pregnancy. Reduction of lifetime lead exposure may be required to decrease risk of fetal exposure.