Low-level maternal exposure to cadmium, lead, and methylmercury and birth outcomes in a Swedish prospective birth-cohort

Abstract

Background: Observational studies have indicated that low-to-moderate exposure to cadmium (Cd), lead (Pb), and methylmercury (MeHg) adversely affects birth anthropometry, but results are inconclusive. Objective: To assess the exposure to Cd, Pb, and MeHg in pregnant women, identify the main dietary sources, and elucidate potential impact on birth anthropometry. Methods: In the NICE (Nutritional impact on Immunological maturation during Childhood in relation to the Environment) birth-cohort in northern Sweden, blood and urine were collected from pregnant women in early third trimester. Cd, Pb and Hg were measured in erythrocytes (n=584), Cd also in urine (n=581), by inductively coupled plasma mass spectrometry. Dietary data were collected through a semi-quantitative food frequency questionnaire administered in mid third trimester. Birth anthropometry data were extracted from hospital records. Results: Bivariate associations appeared non-linear (inverted U-shape). In multivariable-adjusted spline regression models, a doubling of maternal erythrocyte Cd above 0.50 µg/kg (median: 0.29 µg/kg) was significantly associated with reduced birth weight by almost 200 g, and length by 0.7 cm. The association with birth weight remained when the analysis was restricted to never-smokers. Likewise, a doubling of erythrocyte Hg above 1.0 µg/L (median 1.5 µg/kg, mainly MeHg), was significantly associated with 60 g lighter and 30 cm shorter newborns. Maternal Pb (median 11 µg/kg) was unrelated to birth weight and length. Erythrocyte Cd was primarily associated with intake of grains, rice and root vegetables, Pb with tea, coffee and game meat, and Hg with intake of fish. Conclusion: The results showed that low-level maternal Cd and MeHg exposure during pregnancy was associated with poorer birth anthropometry. The indicated positive associations at very low exposure levels, likely reflected food benefits. Further prospective studies in low-level exposed populations are warranted.