Vitamin D concentrations during pregnancy and in cord blood: a systematic review and meta-analysis

Context: Effect size estimates for the association between vitamin D concentrations in maternal blood during pregnancy and in cord blood vary widely across studies, but no meta-analysis has been conducted to ascertain this association. Objective: The aim of this systematic review was to estimate the pooled effect size for the association between circulating 25-hydroxyvitamin D (25[OH]D) concentrations, a marker of vitamin D status, in maternal blood during pregnancy and in cord blood. Data Sources: The PubMed, Embase, and Web of Science databases were searched from their inception to February 2021. Data Extraction: Following the application of prespecified inclusion and exclusion criteria, 94 articles were eligible for full-text review, which was conducted by 2 authors independently. A third author was consulted when necessary and consensus reached. In total, 26 articles, which comprised 30 studies and 6212 mother-infant dyads, were included. Methodological quality was assessed using a modified version of the Joanna Briggs Institute’s Critical Appraisal Checklist for Studies Reporting Prevalence Data. Correlation coefficient (r) values for the association between maternal serum 25(OH)D concentrations during pregnancy and in cord blood were extracted. Data Analysis: The r values were pooled using random-effects meta-analyses. Sensitivity and subgroup analyses were performed to investigate sources of heterogeneity. The pooled r for all studies was 0.72 (95%CI, 0.64–0.79), indicating high heterogeneity (I2 = 95%, P < 0.01). After influential and outlier studies were removed, the pooled r for 9 studies was 0.70 (95%CI, 0.66–0.74), which resulted in a substantial reduction in heterogeneity (I2 = 41%, P=0.10). Conclusion: The findings support a positive and large correlation between maternal vitamin D concentrations during pregnancy and vitamin D concentrations in cord blood. Systematic Review Registration: PROSPERO registration number CRD42021273348