The active form of vitamin D (calcitriol) has many roles in female reproduction. Bound to its receptor, calcitriol is able to control the genes involved in making estrogen.v The uterine lining produces calcitriol in response to the embryo as it enters the uterine cavity, shortly before implantation. Calcitriol controls several genes involved in embryo implantation. Once a woman becomes pregnant, the uterus and placenta continue to make calcitriol, which helps organize immune cells in the uterus, so that infections can be fought without harming the pregnancy. Poor vitamin D status has been associated with certain pregnancy complications such as gestational hypertension and diabetes.
Women about to undergo in vitro fertilization (IVF) can provide valuable insight into the role of vitamin D, since it is possible to examine each aspect of reproduction, from egg development to implantation of the embryo. A recent study found that women with higher vitamin D levels were significantly more likely to achieve pregnancy from IVF compared to women with lower levels of vitamin D.
Women diagnosed with infertility during the vitamin D exposed period had an 87% higher chance of having a live birth in the 12 months following their diagnosis, compared to women diagnosed later, during the non-exposed period. Women diagnosed during the transitional, wash-out period also had an increased (52% higher) chance of live birth compared to unexposed women.
