Pregnancy Outcomes and Vitamin D Status in the Pacific Northwest
Authors: Thiele Doria K , Erickson Elise , Snowden Jonathan 
Published: November 2023

Introduction

Maternal nutritional status during pregnancy has the potential to impact disease states in the mother and offspring. Research suggests that pregnancies complicated by vitamin D deficiency are more likely to result in gestational diabetes, preeclampsia, cesarean section, and small for gestational age infants. However, findings are mixed and confounding remains a problem. Despite the growing body of literature demonstrating the importance of vitamin D on health, it is not yet recommended that routine serum vitamin D (25[OH]D) analysis be completed. The objective of this study was to describe health outcomes for women and infants related to vitamin D status in pregnancy. Analyzing the impact of pregnancy vitamin D levels on maternal and infant outcomes has the potential to inform clinical practice if morbidity and health care costs could be mitigated.

Methods

A retrospective chart review was completed to extract data from 2 out‐of‐hospital midwifery practices in the Pacific Northwest (Latitude 45.5°N and 47.6°N) between 2010 and 2013. These clinics routinely performed 25[OH]D serum analysis on all patients entering prenatal care. Using a low‐risk population allows for determination of impact of vitamin D status in the absence of other factors that can confound results. Inclusion criteria were pregnant women receiving prenatal care in either practice who had 25[OH]D analysis prior to 36 weeks gestation.

Results

A total of 237 participant charts were included in the analysis. Descriptive statistics include 85% of the sample was white race, mean age was 30.8 years, 50% were having their first baby, and 43% were overweight or obese with the mean pre‐pregnancy BMI of 24.5. The mean gestation at which serum vitamin D analysis was completed was 13.6 weeks, with more instances occurring in the spring than summer. There was an overall cesarean rate of 10%, only 3 participants delivered prior to 37 weeks gestation, and the mean birth weight was 3577 grams. The mean 25[OH]D level was 31.33 ng/mL and 48% of the population was vitamin D sufficient (>30 ng/mL). Vitamin D status was predicted by location with lower vitamin D levels found at higher latitude, and prepregnancy BMI with a negative relationship, while controlling for race and season. Vitamin D status did not predict pregnancy outcome, gestation at delivery, or mode of delivery. Rates of gestational diabetes and preeclampsia were very low and were not impacted by vitamin D status.

Conclusion

There is a high rate of maternal vitamin D deficiency and insufficiency among healthy, white women in the Pacific Northwest. This is related to latitude and BMI, but not by season, which reflects the inability to produce adequate vitamin D in the skin year round. Despite having a high rate of vitamin D insufficiency and deficiency, this otherwise healthy population saw very low rates of cesarean section, gestational diabetes, preeclampsia, and preterm birth or small for gestational age. This likely reflects the overall good health of our study population, and the ability of the body to compensate for vitamin D deficiency and confirms the complexity of these outcomes.

Support or Funding Information

Sigma Theta Tau Beta Psi Chapter Naomi Ballard Nursing Research Grant (Thiele)