The role of vitamin D in pregnancy and lactation; emerging concepts by Carol Wagner et al. provides a thorough summary. The full paper is available for the public. Wagner discusses many aspects of vitamin D and pregnancy including the differences in vitamin D metabolism during pregnancy, as opposed to non-pregnant; the future effects on the baby; vitamin D's immune effects during pregnancy; and an overview of her randomized controlled trials with vitamin D and pregnancy.

The conclusion is that pregnant women should get their 25(OH)D serum level up to 40 ng/ml as early as possible in their pregnancy, and remain there throughout for an optimal pregnancy and fetus. Ideally, before they even get pregnant.

It is even better to have a 40 ng/ml or higher vitamin D level during preconception!  In a recent study published by Dr. Mirzakhani et al., they had zero instances of preeclampsia IF the woman came into her first visit with a vitamin D serum level of 40 ng/ml or above.

How does Vitamin D effect the immune system of the child?

You may not call it respiratory syncytial virus (RSV) when your child has cold-like symptoms, bronchitis, or pneumonia - but that is the virus which typically causes those conditions in the lungs. Since sickness in early life can be very serious, or even fatal, a set of researchers decided to study the role of vitamin D in utero on the incidence of these infections during the first year of life.

Mirjam E. Belderbos et al. enlisted mothers in a birth cohort in Utrecht, Netherlands. They studied 156 babies who were all born healthy and full term (37 weeks or later). Cord blood was taken at birth for study and a consultation was done with the parents between 1 and 3 weeks of age. Parents kept a daily log for one year to report any symptoms. If any cough or wheeze lasted for 2 days parents were instructed to get a sample via swab and send it to the lab. Physician reports were also used if the baby was brought to the doctor. 

Analyzing the number of infections by vitamin D serum level found that babies with cord blood less than 20 ng/ml were 6.2 times more likely to have an infection compared to babies with cord blood greater than or equal to 30 ng/ml. The study also found an association between vitamin D levels in the mother and the child as well as a clear seasonal variation in vitamin D levels - with those born in the summer having the highest levels. 

How does vitamin D effect brain development in the child?

Andrew Whitehouse et al. set out to determine whether vitamin D sufficiency in pregnancy during a critical time window of brain development had an effect on brain development during childhood. They studied behavioral, emotional and language development.

Vitamin D levels were measured for 743 women at 18 weeks pregnancy in Perth, Australia and their measurements were put into four different groups (6-18 ng/ml, 19-23 ng/ml, 24-28 ng/ml, 29-62 ng/ml). The children were then measured using industry standard checklists for behavior, emotional and language development at ages 2, 5, 8, 10, 14, and 17 years.

They did not find a significant difference in behavior and emotional difficulties. But, there was a significant difference in language impairment. Children whose mothers had vitamin D levels in the lowest group, 6- 18 ng/ml, were twice as likely to have difficulties in language development as compared to the children whose mothers had vitamin D levels in the highest group, between 29 and 62 ng/ml.

How does vitamin D effect future type 1 diabetes diagnosis 30 years later?

Elina Hyppönen et al. wanted to find out how vitamin D in very early childhood would effect health later in life. In this case over 12,000 women in Oulu and Lapland, Northern Finland were enrolled in a birth cohort in 1966. The recommended dose of vitamin D for infants at the time was 2000 IU D per day. During that first year of life data was collected on how much vitamin D the children received and if any rickets was experienced.

After year one, 10,821 children had complete data. 30 years later, in 1997-1998, a follow up survey was sent to these participants. The main outcome they were searching for was whether this individual had been diagnosed with type 1 diabetes. For this group, 81 people had been diagnosed with type 1 diabetes, at a median age of 14 years. The conclusion was that the children who received regular supplementation of at least 2000 IU/day had an 80% lower risk of type 1 diabetes at 30 years old than the children who received less.