The purpose of the present study is to understand the effect of pregnancy on vitamin D metabolism and requirements as well as the modulatory role of the placenta in vitamin D metabolism during pregnancy. In addition, a human placental cell culture model will be employed to examine vitamin D metabolic flux in human trophoblast cells. The impact of maternal vitamin D status on maternal and fetal bone health during gestation will also be examined.

Rationale

Despite mounting evidence that maternal vitamin D status is linked to pregnancy outcomes [1,2], the impact of pregnancy on vitamin D metabolism and requirement has yet to be clearly defined. In addition, although the placenta is known to express all components of the vitamin D metabolic pathway [3,4], very little is known about placental vitamin D metabolism. Moreover, although vitamin D is known to affect bone health in the nonpregnant state, the effect of maternal vitamin D status on maternal and fetal bone health in human pregnancy is unclear [5-7]. Therefore, the present study seeks to advance current understanding of vitamin D metabolism and requirements during pregnancy.

Objective and Research Questions

This study aims to examine: 1) the effect of pregnancy on a comprehensive panel of blood biomarkers of vitamin D status and metabolism; 2) the role of the placenta in modulating circulating vitamin D metabolites; and 3) the impact of maternal vitamin D status on maternal and fetal markers of bone metabolism.

Study Population, Design, and Exposure

As a secondary analysis, this study uses biological samples obtained from pregnant and nonpregnant control women who participated in a 12-wk randomized controlled trial in 2009-2010 which featured two doses of choline (i.e., 480 or 930 mg choline/d) (NCT01127022) [8]. Throughout the controlled feeding period, 26 third-trimester pregnant women and 21 nonpregnant women (both reproductive groups aged > 21 y) in a good health status consumed equivalent intakes of vitamin D (511 IU/d), calcium (1.6 g/d) and phosphorus (1.9 g/d) from the study diet and prenatal multivitamin supplement (Pregnancy Plus; Fairhaven Health LLC) for ≥ 10 weeks.

Dependent variables:

1. Blood biomarkers of vitamin D metabolism at week 0 (study-baseline) and week 10 (representing study-end)
2. Placental biomarkers of vitamin D metabolism at delivery
3. Markers of bone metabolism in maternal and fetal cord blood as well as maternal urine

Ethical considerations

The study protocol of the original RCT was approved by the Institutional Review Board for Human Study Participant Use at Cornell University and the Cayuga Medical Center where pregnant women delivered their babies. Informed consent was obtained from all participants before study entry, and the original study was registered at clinicaltrials.gov as NCT01127022. For this secondary analysis, deidentified data will be used.

Dissemination Findings

Findings from the present study will be reported in manuscripts that will be submitted for publication to a leading medical/nutrition journal in an appropriate field (i.e. nutrition, bone, placenta, and reproductive physiology). In addition, findings will be presented as abstracts, posters, and presentations at research conferences.

Inclusion Criteria:

• Age of 21-40 y
• Healthiness as assessed by health-related questionnaire, a blood chemistry profile, and a complete blood count
• Normal liver and kidney function
• Willingness to comply with the study protocol
• Singleton pregnancy (pregnant women only)

Exclusion Criteria:

• Use of tobacco, drug, or alcohol
• Use of prescription medications known to affect liver function
• Pregnancy associated complications

The study population consists of all healthy third-trimester pregnant (n=26) and nonpregnant (n=21) women who participated in the original RCT study.