Pregnancy is a high-risk condition. Some of the more common complications of pregnancy include preeclampsia, small for gestational age (SGA), gestational diabetes mellitus (GDM), and preterm birth. Preeclampsia involves hypertension, protein in the urine, and swelling. If a woman with preeclampsia has a seizure then it becomes eclampsia. SGA are babies that are smaller than they are supposed to be based on the length of the pregnancy. GDM is diabetes that appears during pregnancy and usually resolves after birth. Preterm birth is when the baby comes before his or her due date.
Many observational studies have looked at vitamin D levels during pregnancy and whether levels are associated with these complications. To date, many studies have found an increased risk of these complications with lower levels of vitamin D.
Recently, Dr Shu-Qin Wei and colleagues of the University of Montreal reviewed all the literature on the topic and performed a meta-analysis of these observational studies, to see what all the studies combined found.
The authors screened 2,406 papers to find 24 rigorous studies and combined the results into one meta-analysis. They found that pregnant women with 25(OH)D levels lower than 20 ng/ml had:
- an increased risk of preeclampsia (OR 2.09 of >2200 women in 8 studies),
- an increased risk of gestational diabetes mellitus (OR 1.38 of > 5,600 women in 12 studies)
- an increased risk of preterm birth ([OR 1.58 of > 1,200 women in 5 studies)
- an increased risk of small-for-gestational age (OR 1.52 of > 6,000 women in 6 studies)
The damage done to mother and baby via vitamin D deficiency is widespread and involves widely different mechanisms of action. There is evidence that vitamin D affects placental function, glucose control, infection and inflammatory response. The increased inflammatory of maternal vitamin D deficiency includes increased production of proinflammatory cytokines, such as tumor necrosis factor, interleukin-6, and interferon gamma. Maternal vitamin D deficiency has also been associated with insulin resistance and impaired insulin secretion.
If you are pregnant, or know someone who is pregnant, start taking at least 5,000 IU/day of vitamin D. The evidence for this recommendation does not just stem from just these observational studies but rather also from a few randomized controlled trials that have shown vitamin D supplementation at 4,000 to 5,000 IU/day during pregnancy is safe and healthy.