Abstract:
Background
Three previous reviews on the association of vitamin D insufficiency in pregnancy with pre-
term birth (PTB) and stillbirth were limited in scope and deemed inconclusive. With impor-
tant new evidence accumulating, there is the need to update the previous estimates and
assess evidence on other clinically important outcomes such as spontaneous abortion and
Apgar score. We conducted a systematic review and meta-analysis to evaluate the quality
and strength of the available evidence on the relations between vitamin D nutritional status,
and pregnancy and birth outcomes.
Methods
PubMed and Scopus databases were searched from their inception to June, 2015 with no
language restrictions imposed. Eighteen longitudinal studies satisfied the inclusion criteria.
Random effects model was applied in computing the summary effect estimates and their
corresponding 95% confidence intervals.
Results
Serum 25(OH)D levels <75 nmol/l was associated with 83% (95% CI: 1.23, 2.74) and 13%
(95% CI: 0.94, 1.36) increased risk of PTB measured at <32–34 weeks and <35–37 weeks,
respectively. An inverse dose-response relation was observed for both PTB outcome.
Serum 25(OH)D levels <75 nmol/l was also associated with 11% increased risk of spontane-
ous PTB (<35–37 weeks; RR = 1.11; 95% CI: 0.75, 1.65) with a dose-response relation also
noted. Vitamin D insufficiency was not associated with risk of spontaneous abortion and still-
birth (RR of 1.04 [95% CI: 0.95, 1.13] and 1.02 [95% CI: 0.96, 1.09], respectively), as well as
short gestational length (ES = -0.24, 95% CI: -0.69, 0.22), and low Apgar score.
Conclusions
We found vitamin D insufficiency to be associated with risk of PTB. Regarding spontaneous
abortion and stillbirth, the available evidence suggest no association with low vitamin D lev-
els. The evidence on vitamin D nutrition and Apgar score is conflicting and controversial.
Overall, the experimental evidence uncovered was small and weak. Hence, the benefits of
vitamin D supplementation during pregnancy should be further evaluated through rigorous
intervention studies.
