BACKGROUND AND PURPOSE: 

• There are previous studies showing that vitamin D deficiency may be related to adverse obstetrical outcomes 
  • Recent Cochrane review of prenatal vitamin D supplementation (see ‘Related ObG Topics’ below) found that vitamin D, compared with no intervention or placebo, reduced the risk of preterm birth and may lower risk of preeclampsia  
• Gernand et al. (BJOG, 2017) examined the correlation between maternal vitamin D status and risk of preeclampsia and preterm birth in women at high-risk for preeclampsia 

METHODS: 

• Analysis of prospectively collected data and blood samples from a trial of prenatal low-dose aspirin in women at high risk for preeclampsia (multicentered MFMU study) 
• 25-hydroxyvitamin D [25(OH)D] concentrations were measured from stored maternal serum samples drawn at 12–26 weeks’ gestation (n= 822) 
  • Used multiple cut-points of 30, 50, and 75 nmol/l (which correspond to 12, 20, and 30 ng/ml, respectively) 
• Primary outcomes were preeclampsia and preterm birth 
• Mixed effects models were used to control for confounders including prepregnancy BMI and race 

RESULTS: 

• Majority were non-Hispanic black (62.8%), parous (77.6%), 20–29 years old (56.1%), not married (63.4) and non-smokers (83.2%) 
• 12% of women were vitamin D deficient [25(OH)D <30 nmol/l] 
• Compared to women with 25(OH)D ≥75 nmol/l (highest cut-point level) 
  • Women with 25(OH)D <30 had a 2.4-fold (95% CI 1.0–5.6) higher risk of early-onset pre-eclampsia (<35 weeks’ gestation) 
  • Women with 25(OH)D <50 nmol/l had a 1.8-fold (95% CI 1.0–3.2) increased risk of preterm birth at <35 weeks, mostly driven by indicated preterm births  
• No association between vitamin D status and preeclampsia or preterm birth at <37 weeks was observed 

CONCLUSION: 

• Low levels of maternal vitamin D status in the second trimester were associated with higher risk of early-onset pre-eclampsia and preterm birth at <35 weeks in women at high risk for pre-eclampsia 
• The authors are in agreement with Cochrane Review that more rigorous studies are need to determine causation and if supplementation is effective

Learn More – Primary Sources:  

Vitamin D, pre-eclampsia, and preterm birth among pregnancies at high risk for pre-eclampsia: an analysis of data from a low-dose aspirin trial

Related ObG Topics:

Do Vitamin D and Calcium Supplements Decrease Cancer Risk?

(Cochrane 2016) Vitamin D During Pregnancy and Adverse Pregnancy Outcomes

Does Vitamin D Decrease Risk of Respiratory Infections?