Maternal influences on cord blood lead levels.

We constructed models of umbilical cord blood lead (PbB), with and without the addition of maternal PbB at delivery and earlier in pregnancy, to determine which factors explaining cord PbB depended upon maternal PbB and which did not. We prospectively studied women of low-to-middle socioeconomic status who lived in the Valley of Mexico from 12 weeks of pregnancy to delivery. We measured maternal venous PbB during pregnancy and at delivery, and umbilical cord PbB (1-38 micrograms/dl, 0.05-1.83 mumol/l). We used multiple regression analyses to model cord PbB and a logit analysis to model the maternal-cord PbB relationship. Older mothers using lead-glazed pottery and canned foods delivered babies with increased cord PbB, while those with occasional alcohol use during pregnancy, high milk intake, and more spontaneous abortions delivered babies with lower cord PbB. Maternal PbB at 36 weeks of pregnancy and at delivery independently explained additional variance in cord PbB, but maternal PbB earlier in pregnancy did not. Some of the effects of lead-glazed pottery, maternal abortions, alcohol use, and canned food use on cord PbB were mediated through maternal PbB. The effects of maternal age and milk intake on cord PbB were independent of their influence on maternal PbB near delivery. Cord PbBs were higher than maternal PbBs at delivery in 33% of the cases, and were predominant in mothers over 30 and those drinking milk less than once per day. Measurable influence of maternal PbB on delivery cord PbB is limited to the four to eight weeks prior to delivery. Many factors suspected of influencing bone lead also control cord PbB, some of them independently of their effect on maternal delivery PbB. Minimizing fetal exposure near the end of pregnancy may require long-term control of maternal lead exposure and good management of pregnancy and diet.