Emerging evidence from animal studies has established tributyltin (TBT) as a novel environmental obesogen in the development of obesity and impaired metabolic function. However, data on health effects of TBT exposure in humans are lacking, indicating a critical and urgent need to translate the findings from animal studies to humans. This project is innovative in being the first to investigate the associations of prenatal TBT exposure during early pregnancy with maternal obesity and gestational weight gain. The Investigators will measure TBT concentrations in maternal plasma samples collected from 100 pregnant women at the first prenatal visit (<10 weeks of gestation). These samples have been already collected and archived in the University of Iowa Maternal Fetal Tissue Bank, an ongoing prospective cohort study. Maternal anthropometric measures, along with demographic and clinical data, will be extracted from confidential electronic health records.