RecruitingClinical trialVitamin D Dynamics in WomenThe goal of this project is to utilize stable isotopically labeled vitamin D3 and state of the art mass spectrometric methodology to assess vitamin D dynamics during pregnancy in relation to relation to obesity and vitamin D binding protein genotype. At the conclusion of this study, the investigators will have obtained novel information on the absorption and utilization of vitamin D in women and the degree to which vitamin D utilization during pregnancy is impacted by genetic ancestry, vitamin D binding protein concentration and genotype and by excess adiposity. The long-term goal is to better understand the unique metabolism of vitamin D during pregnancy.