Introduction Vitamin D deficiency has developed into a public health problem in recent years in the United States. With more people likely suffering from vitamin D deficiency or insufficiency due to decreased milk consumption, increased UV protective sunscreens, and decreased sun exposure. This is particularly concerning for women of childbearing age, as many nutritional deficiencies during pregnancy are often associated with adverse outcomes for the mother and the developing fetus. Vitamin D, known as calcitriol in its active form, is vital for calcium homeostasis and a variety of vitamin D-dependent gene transcriptions in humans. Vitamin D deficiency during pregnancy has been linked to impaired bone development and rickets (1). Furthermore, recent findings suggest that vitamin D deficiency may also be associated with asthma and type 1 diabetes (1). Recent research has studied the effects of vitamin D supplementation, particularly during pregnancy. However, there is still no clear recommendation on taking vitamin D during pregnancy. The current recommended DRI of vitamin D for pregnant women is an adequate intake (AI) of 15 µg/day (400 IU), with a tolerable upper intake level (UL) of 100 µg/day (4000 IU) ( 2). It is estimated that as many as 41.6% of US adults are deficient or insufficient in vitamin D, prompting many to suggest supplementation interventions (3). There is much evidence demonstrating the effects of vitamin D deficiency or insufficiency during pregnancy, but even less is known about the consequences of increased vitamin D intake due to supplementation. The purpose of this article is to determine whether high-dose vitamin D supplementation increases the risk of adverse maternal or fetal outcomes. Methods The following methods were used to retrieve studies used in analyzing the effects of high-dose vitamin D