The importance of vitamin D during pregnancy

- from the first trimester

A pregnant woman's vitamin D level in the first trimester is relevant for the development and growth of the fetus. According to a study published in The American Journal of Clinical Nutrition, being vitamin D-deficient during the first trimester can increase the risk of preterm birth and decreased birth length.

The new study was led by nutrition researcher Celeste Beck, who is affiliated with Pennsylvania State University in the USA. Previous studies have shown that vitamin D is important for the development of the placenta, as well as the baby’s bones, immune system, and nervous system. However, most studies of the importance of vitamin D for fetal development have been conducted from the second trimester onwards. Since more than 25% of pregnant and breastfeeding women are vitamin D-deficient, Celeste Beck and her research team set out as the first to examine how vitamin D affects early pregnancy and the baby’s later development.
Together with colleagues from the University of Utah, the research team analyzed blood samples from 351 women, who were already participating in another long-term study (Nulliparous Pregnancy).
The vitamin D levels of the pregnant women were measured in nmol/L (nanomoles per liter), with 50 nmol/L being considered the lower limit, whereas the ideal level is above 75 nmol/L.
The study revealed that pregnant women with vitamin D levels below 40 nmol/L had four times the risk of preterm birth compared to those with levels above 80 nmol/L. However, since only a few participants delivered preterm, larger studies are required in this area.
The researchers also observed a correlation between vitamin D levels in the blood and the infant length. Pregnant women with the highest levels of vitamin D in their blood could expect their babies to be statistically significantly longer at birth.
When the researchers examined the vitamin D levels in the second trimester, no differences were observed with regard to the baby’s growth or other parameters. It also turned out that more pregnant women had optimal vitamin D levels in the second trimester. However, further research is needed.
In any case, the study shows that diet and lifestyle play a crucial role in fetal development, starting from early pregnancy.

Relevant supplements during pregnancy

Since diet only provides a small amount of vitamin D, it is especially important to get enough sunlight during the summer and to take supplements during the winter months. It is also recommended that pregnant and breastfeeding women take vitamin D supplements all year round to support both the baby’s growth and the mother’s health.
According to Celeste Beck and her research team, vitamin D is crucial throughout pregnancy, alongside iron, folic acid, and other nutrients.
Women planning to become pregnant should also make sure to be properly supplied with vitamin D. A blood sample to determine the vitamin D level may be a good idea, as individual needs can vary.

References:

Celeste Beck et al. Maternal vitamin D status, fetal growth patterns, and adverse pregnancy outcomes in multisite prospective pregnancy cohort. The American Journal of Clinical Nutrition. 2025

Penn State. Vitamin D matters during first semester. ScienceDaily 2025