The critical fetal stage for maternal manganese exposure

Prenatal exposure and the health effects of that exposure have been intensively studied for a variety of environmental pollutants and trace elements. However, few studies have compared susceptibilities among the three trimesters of gestation. Manganese (Mn) is a naturally occurring and abundant trace element in the environment. Although the effects of Mn on animals are well documented, knowledge of the effects of Mn exposure on pregnant women and fetuses remains limited. A longitudinal study was conducted by collecting blood samples during all three trimesters, and Mn exposure was completely characterized during gestation. The aims of this study were to examine the effects of maternal Mn exposure on neonatal birth outcomes and to explore the critical stage of these effects. In total, 38, 76 and 76 samples were obtained from singleton pregnant women in their first, second and third trimesters, respectively. The cohort of pregnant women was selected at a medical center in northern Taiwan. Erythrocyte samples were collected during the first, second and third trimesters of gestation. Erythrocyte Mn concentrations were measured by inductively coupled plasma mass spectrometry. Neonatal birth outcomes were evaluated immediately after delivery. A multivariate regression model was used to determine the associations between maternal Mn levels in erythrocytes in each trimester and neonatal birth outcomes. The geometric mean concentrations of Mn were 2.93 μg/dL, 3.96 μg/dL and 4.41 μg/dL in the first, second and third trimesters, respectively. After adjusting for potential confounders, a consistently negative association was found between maternal Mn levels throughout the three trimesters and birth outcomes. Log-transformed Mn levels in maternal erythrocytes in the second trimester were significantly associated with neonatal birth weight, head and chest circumferences, respectively (β=-556.98 g, p=0.038; β=-1.87 cm, p=0.045; β=-2.74 cm, p=0.024). Despite the limited sample size in the first trimester, negative effects of maternal Mn levels on birth weight (β=-1108.95 g, p<0.01) and chest circumference (β=-4.40 cm, p=0.019) were also observed.