Urinary excretion of lead during pregnancy and postpartum

We have compared lead isotopic ratios and lead concentrations in 53 spot ur ine and 59 24-h urine samples from 13 subjects covering the interval from p re-pregnancy through 180 days postpartum to estimate the amount of lead exc reted in urine and renal clearance relative to blood. The total amount of l ead excreted in 24-h urine samples ranges from 0.8 to 5.9 mu g Pb with an a rithmetic mean of 2.2 +/- 1.1 mu g (geometric mean 1.90 mu g). This compare s with amounts of 0.9-10 mu g of extra lead per day estimated to be release d into blood from the skeleton during pregnancy and postpartum. There were no differences in excretion rates during the trimesters of pregnancy and be tween pregnancy and postpartum time periods. The renal clearance relative t o blood ranged from 0.8 to 10 g/h (arithmetic mean 3.2 +/- 1.9; geometric m ean 2.7). Renal clearance relative to blood was somewhat higher in trimeste rs 2 and 3 compared with postpartum 150-180 days (P = 0.004, 0.006, respect ively). Reassessment of earlier published blood and dietary data for Austra lian pregnant controls indicates there is no increased gastrointestinal abs orption of lead during pregnancy and postpartum. This differs from calcium, which shows increased absorption during late pregnancy. In light of the in convenience of sampling and potential contamination at the low levels of le ad found in most of these subjects, we do not consider the 24 fi urines to provide sufficient useful information. (C) 2000 Elsevier Science B.V. All r ights reserved.