Vitamin D monitoring during pregnancy and postpartum

A pilot study highlights the global prevalence of vitamin D deficiency during pregnancy and its association with complications like gestational diabetes, preterm birth, and intrauterine growth restriction—despite dietary supplementation and sun exposure.

Study: Effects of Maternal Vitamin D Levels on Prematurity: Feasibility Study in a Multicenter Observational Pilot. Image Credit: Andrey_Popov / Shtuterstock.com

A recent study published in Nutrients determines the impact of vitamin D levels during pregnancy and their role in maternal and infant health outcomes.

The essential role of vitamin D during pregnancy

Low vitamin D levels during pregnancy increase the risk of numerous adverse maternal and infant health outcomes, some of which include intrauterine growth restriction (IUGR), pre-eclampsia, cholestasis, and gestational diabetes which, collectively, can lead to preterm birth.

The prevalence of low vitamin D levels during pregnancy is evident throughout the world, regardless of women residing in nations with high sun exposure like China, Turkey, Iran, and Pakistan. Hypovitaminosis D during pregnancy also persists despite obstetrician recommendations that pregnant women take 400-600 IU/day.

During pregnancy, 25-hydroxyvitamin D [25(OH)D] crosses the placenta and is activated by the fetal kidneys. The placenta can also synthesize the activated form of 25(OH)D to support placental metabolism.

About the study cohort

The current study included 30 pregnant women, 52% of whom were between 25 and 34 years of age. About 53% of study participants had type III skin, which denoted darker white skin that is accompanied by any hair or eye color.

About 40% of the study cohort reported a history of smoking and 43.3% consumed alcohol. Before becoming pregnant, 30% of the study participants were considered overweight, whereas 16.7% were obese.

Over 93% of the study participants regularly consumed a Mediterranean diet, which often included the consumption of vitamin D-rich foods like milk and dairy products. About 40% of mothers were physically active.

Among the study cohort, 93.3% conceived naturally, 30% of whom were experiencing their first pregnancy. Over 62% of the study participants experienced labor dystocia, which prevents the baby from exiting the pelvis due to various reasons, some of which include a small maternal pelvis, large fetus, or failure of the uterus and cervix to contract normally. Over 72% of babies born to these mothers were born by caesarean section.

Over 31% of study participants were diagnosed with gestational diabetes, whereas 18.8% of babies were diagnosed with IGUR. One infant was born preterm at 34 weeks and was subsequently hospitalized in the neonatal intensive care unit (NICU) for five days. About 79% of children were short in length at birth, whereas 51.7% had a small head circumference.

What caused the preterm birth?

The mother of the infant who was born at 34 weeks gestation had previously undergone 25(OH)D testing at 28 weeks. At this time, the mother’s serum 25(OH)D levels were 36 ng/mL, which is considered sufficient 25(OH)D.

However, no data were available for her postpartum 25(OH)D levels. Importantly, this woman had a history of miscarriage and preterm delivery at 33 weeks.

The data were highly heterogeneous due to the lack of blood samples obtained from all study participants at two distinct time points. As a result, 15 study participants only provided a single blood sample within 48 hours postpartum, whereas the remaining 15 study participants provided one blood sample upon entering the study, as well as the postpartum sample. The postpartum sample is crucial, as it confirms the importance of measuring 25(OH)D levels during the postnatal period.

It was very important to ensure that it was possible to carry out [postpartum] vitamin D measurement within 48 hr, since there are scientific publications that show a strong association between maternal and newborn vitamin D levels in this time interval.

Conclusions

The pilot study met all feasibility criteria, thus indicating the effectiveness of this longitudinal model for monitoring 25(OH)D levels throughout the natal and postnatal periods. To overcome the lack of longitudinal data, the researchers are currently conducting a larger study, during which blood samples will be obtained at two distinct time points.

A recruitment rate of over 73% was reported, with an eligible recruitment rate of 88.2%, thus indicating a high level of interest and willingness of patients to participate. Moreover, 100% adherence and retention rates were reported, which further supports the willingness of patients to participate in this type of study.

The environment was conducive to maintaining strong participant engagement and compliance over time.”