Theses and Dissertations

Issuing Body

Mississippi State University


Tidwell, Diane K.

Committee Member

Oliver, Brittney D.

Committee Member

Briley, Chiquita A.

Committee Member

Allsopp, Marie

Committee Member

Williams, Ron D.

Date of Degree


Document Type

Dissertation - Open Access



Degree Name

Doctor of Philosophy


College of Agriculture and Life Sciences


Department of Food Science, Nutrition and Health Promotion


Vitamin D inadequacy is highly prevalent among pregnant women worldwide. Inadequacy or deficiency of vitamin D can lead to adverse outcomes during pregnancy such as pre-eclampsia, gestational diabetes, and caesarian section. A systematic review and meta-analysis were conducted to examine the effectiveness of vitamin D supplementation on serum vitamin D status during pregnancy in randomized controlled trials (RCTs). A search was conducted in PubMed, Scopus, ProQuest, EBSCO, Cochrane CENTRAL Database of Controlled Clinical Trials, PsycINFO, CINAHL, and Google Scholar, in addition to searching reference lists in published reviews. A comprehensive list of RCTs of vitamin D status and supplemental use in pregnancy was compiled. The random effects model was used to determine a summary effect size using pre/post means and standard deviations of serum vitamin D levels from intervention and control groups. Sixteen RCTs indicated a large effect size (d = .849, 95% CI .607 – 1.001, p < .001). Serum vitamin D concentration at delivery was higher with vitamin D supplementation, and thereby the metabolic outlook was favorable for the mother and newborn. Heterogeneity of the meta-analysis was significant (Q = 344.418, p < .001); the I-squared statistic showed moderate heterogeneity (61.89%), which warranted subgroup analysis to identify possible sources of variation among the studies. Moderators for subgroup analysis included vitamin D dosages, use of a placebo, use of multivitamins in addition to vitamin D, duration of interventions, age, low or adequate baseline vitamin D status, trimester when supplementation was started, country where the RCT was conducted (USA/UK/AUS versus other countries), and blinded versus non-blinded RCTs. Subgroup analysis only demonstrated a significant impact on heterogeneity from the trimester moderator (p < .001). Women who began vitamin D supplementation during the first trimester had a higher effect size and improved vitamin D status compared to those who began supplementation in the second or third trimester. Since pregnant women with vitamin D inadequacy or deficiency are more susceptible to complications, routine examination of vitamin D status should be conducted in pregnant women.