Patterns and determinants of blood lead during pregnancy.

The pattern of blood lead during pregnancy was investigated in a cohort of 195 women who, between October 1992 and February 1995, entered prenatal care at Magee-Womens Hospital in Pittsburgh, Pennsylvania, by week 13 of pregnancy. Blood was drawn as many as five times, once in each of the first two trimesters and a maximum of three times in the third trimester. Blood lead determinations were made by atomic absorption spectrophotometry. Potential sources or modifiers of lead exposure were collected by interviews, including sociodemographic, pregnancy history, occupational, and lifestyle data. Results confirmed a previously reported U-shaped curve in blood lead concentration during pregnancy as well as findings that blood lead levels increase with age, smoking, lower educational level, and African-American race and decrease with history of breastfeeding and higher intake of calcium. Additionally, interactions were found between time since last menstrual period and both maternal age and calcium. Specifically, older mothers showed steeper increases in blood lead concentrations during the latter half of pregnancy than did younger mothers, and intake of calcium had a protective effect only in the latter half of pregnancy, an effect that became stronger as pregnancy progressed. These findings provide further evidence that lead is mobilized from bone during the latter half of pregnancy and that calcium intake may prevent bone demineralization.