Prenatal exposure to essential and toxic elements in relation to infant growth trajectories

Metal exposures have been associated with adverse growth in utero, but impacts on postnatal growth are not well-understood. To examine relationships between prenatal metal exposures and infant growth trajectories in a rural U.S. pregnancy cohort. Participants included 783 mother-infant pairs in the New Hampshire Birth Cohort Study, a rural cohort of pregnant people and their children in northern New England with homes served by private unregulated drinking water. Essential and toxic element concentrations were measured in maternal toenail clippings collected at 3 weeks postpartum, reflecting exposures during pregnancy. Weight and length measures were abstracted from medical records between birth and 18 months. Weight-for-length growth trajectories were identified separately for male and female infants using growth mixture modeling. Relative risk ratios and 95% confidence intervals were estimated to evaluate associations between each element and growth trajectory assignments. Four weight-for-length trajectories were identified for male and female infants: Stable-slow, Late-moderate, Stable-moderate, and Rapid growth. The Stable-slow trajectory aligned most closely with the median World Health Organization infant growth curve and was selected as the reference. Among male infants, higher maternal mercury and lead were each associated with a higher likelihood of following a growth pattern that deviated from the reference. Additionally, male infants whose mothers fell in the lowest tertile for manganese, compared with the middle tertile, were more likely to follow the Stable-moderate growth trajectory, rather than the reference. No statistically significant associations were identified for female infants. Growth during the first 18 months of life may be accelerated in male infants exposed to higher levels of mercury or lead or to lower levels of manganese in utero. Given that accelerated growth during infancy increases risk for obesity, male infants who experience these element exposure patterns may be more susceptible to obesity later in life.