Vitamin D deficiency is associated with gestational diabetes and preeclampsia. Vitamin D is well known to support bone growth but it can also improve insulin resistance and glucose tolerance. 40-60% of the U.S. population is vitamin D deficient, including pregnant mothers. Most prenatal vitamins contain only 600IU. The dosage is low because 10,000 IU/day may lead to toxicity. However, recent studies show 1000-4000 IU per day of vitamin D is a preferred dosage for mothers low in vitamin D and taken at this level it has proven to improve blood glucose levels.