High Prevalence of Maternal Serum 25-Hydroxyvitamin D Deficiency Is Not Associated With Poor Birth Outcomes Among Healthy White Women in the Pacific Northwest

Objective: To quantify vitamin D status among pregnant women in the Pacific Northwest (Portland, OR, and Seattle, WA) and examine pregnancy and newborn outcomes in relationship to maternal serum blood samples obtained during pregnancy. Design: A retrospective cohort design. Setting: Data from 2009 to 2013 were abstracted from the health records of two out-of-hospital midwifery practices in the Pacific Northwest. Participants: Women with recorded serum blood samples for vitamin D during pregnancy were included. We reviewed health records of 663 women, and 357 met criteria. Methods: We extracted demographic, biometric, and pregnancy outcome data from participants’ records and analyzed them using regression models. Results: Mean serum 25-hydroxy vitamin D (25[OH]D) was 29.96 ± 10.9 ng/ml; 45.5% of participants were sufficient (≥30 ng/ml), and 55.5% were insufficient or deficient (<29 ng/ml). Lower vitamin D levels were predicted by Seattle location, greater prepregnancy body mass index, and blood samples drawn during the winter. Vitamin D status was not a predictor of spontaneous abortion, glucose tolerance test result, cesarean birth, infant birth weight, or any other outcome investigated. Conclusion: Although there is a high prevalence of vitamin D insufficiency and deficiency in pregnant women in the Pacific Northwest, adverse health effects were not observed. This may be attributable to the overall healthy profile of the women in our sample. Further research on maternal vitamin D status should focus on identification of optimal vitamin D levels in pregnancy and long-term outcomes among offspring of women who are vitamin D deficient, particularly those from high-risk, vulnerable populations.