Urinary excretion of lead during pregnancy and postpartum

We have compared lead isotopic ratios and lead concentrations in 53 spot urine and 59 24-h urine samples from 13 subjects covering the interval from pre-pregnancy through 180 days postpartum to estimate the amount of lead excreted in urine and renal clearance relative to blood. The total amount of lead excreted in 24-h urine samples ranges from 0.8 to 5.9 microg Pb with an arithmetic mean of 2.2+/-1.1 microg (geometric mean 1.90 microg). This compares with amounts of 0.9-10 microg of extra lead per day estimated to be released into blood from the skeleton during pregnancy and postpartum. There were no differences in excretion rates during the trimesters of pregnancy and between pregnancy and postpartum time periods. The renal clearance relative to blood ranged from 0.8 to 10 g/h (arithmetic mean 3.2+/-1.9; geometric mean 2.7). Renal clearance relative to blood was somewhat higher in trimesters 2 and 3 compared with postpartum 150-180 days (P = 0.004, 0.006, respectively). Reassessment of earlier published blood and dietary data for Australian pregnant controls indicates there is no increased gastrointestinal absorption of lead during pregnancy and postpartum. This differs from calcium, which shows increased absorption during late pregnancy. In light of the inconvenience of sampling and potential contamination at the low levels of lead found in most of these subjects, we do not consider the 24 h urines to provide sufficient useful information.