Vitamin D and risk of preterm birth: Up-to-date meta-analysis of randomized controlled trials and observational studies.
OBJECTIVE
We performed a meta-analysis of randomized controlled trials (RCT) and observational studies to answer the two following questions: (i) whether low maternal circulating 25 hydroxyvitamin D (25-OHD) is associated with an increased risk of preterm birth (PTB) or spontaneous PTB (sPTB); and (ii) whether vitamin D supplementation alone during pregnancy can reduce the risk of PTB.


METHODS
Literature search was carried out using Pubmed, Web of Science and Embase databases up to June 2016. Pooled OR or relative risk (RR) with 95%CI were computed using fixed or random effects models depending on the size of heterogeneity. Subgroup analysis was used to explore potential sources of between-study heterogeneity. Publication bias was evaluated using Egger's test and Begg's test.


RESULTS
Twenty-four articles (six RCT and 18 observational studies) were identified. Maternal circulating 25-OHD deficiency (pooled OR, 1.25; 95%CI: 1.13-1.38) rather than insufficiency (pooled OR, 1.09; 95%CI: 0.89-1.35) was associated with an increased risk of PTB, and vitamin D supplementation alone during pregnancy could reduce the risk of PTB (pooled RR, 0.57; 95%CI: 0.36-0.91). This was also the case for the sPTB subgroup (circulating 25-OHD <50 vs >50 nmol/L; pooled OR, 1.45; 95%CI: 1.20-1.75).


CONCLUSIONS
Maternal circulating 25-OHD deficiency could increase PTB risk and vitamin D supplementation alone during pregnancy could reduce PTB risk. Extrapolation of the results, however, must be done with caution, and there is urgent need for larger, better-designed RCT to confirm this effect.
Department of Maternal, Child and Adolescent Health, Anhui Medical University, Hefei, China.
Shan-Shan
SS
Zhou
Anhui Provincial Key Laboratory of Population Health and Aristogenics, Anhui Medical University, Hefei, China.
Yong-Hao
YH
Tao
Anhui Provincial Key Laboratory of Population Health and Aristogenics, Anhui Medical University, Hefei, China.
Kun
K
Huang
Anhui Provincial Key Laboratory of Population Health and Aristogenics, Anhui Medical University, Hefei, China.
Bei-Bei
BB
Zhu
Anhui Provincial Key Laboratory of Population Health and Aristogenics, Anhui Medical University, Hefei, China.
Fang-Biao
FB
Tao
D000328:Adult; D005260:Female; D006801:Humans; D064887:Observational Studies as Topic; D047928:Premature Birth / Q000097:blood* / Q000517:prevention & control*; D016032:Randomized Controlled Trials as Topic; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood / Q000627:therapeutic use*; D014808:Vitamin D Deficiency / Q000097:blood* / Q000188:drug therapy
D014807:Vitamin D; C104450:25-hydroxyvitamin D
meta-analysis; pregnancy; premature birth; randomized controlled trial; vitamin D