Failure to recruit adequate patients

Demonstrate dose-dependent relationship between vitamin D supplementation and rates of gestational diabetes.

Determine the effect of increased vitamin D supplementation (4000 IU vitamin D3 +prenatal vitamin) on the incidence of gestational diabetes compared to a standard prenatal vitamin among pregnant women at high risk for gestational diabetes.

Explore the effect of increased vitamin D supplementation (4000 IU daily + prenatal vitamin), compared to a standard prenatal vitamin, on glycemic control, need for oral hypoglycemic agents and/or insulin, and delivery outcomes among the subset of women who develop gestational diabetes.

Inclusion Criteria:

1. Women who are currently pregnant and receiving prenatal care at the Women's Health Specialists Clinic (University of Minnesota Physicians) from either MD/DO or CNM providers

2. Subject established prenatal care no later than the completed 12th week of gestation (12 6/7 weeks)

3. Subject possesses as least one of the following characteristics:

   1. BMI greater than or equal to 30 kg/m2
   2. History of gestational diabetes in a prior pregnancy
   3. History of infant with birth weight of 4500g or greater

4. Subject is capable of giving informed consent

Exclusion Criteria:

1. Age less than 18 years

2. Multiple gestation pregnancies (twins, triplets or greater multiples)

3. Vitamin D deficiency (defined as less than 20 ng/mL)

4. Preexisting diabetes mellitus defined as either:

   1. pre-existing diagnosis prior to current pregnancy
   2. failure of three-hour glucose tolerance test in first trimester of pregnancy