Higher serum levels of 25-hydroxyvitamin D (25[OH]D]) may be associated with a reduced risk of spontaneous abortion, according to a new study published in BMC Public Health. The analysis aimed to determine a potential causal relationship between vitamin D levels and spontaneous abortion using a two-sample Mendelian randomization (MR) analysis.

The researchers utilized genome-wide association study summary data from over 500,000 individuals to assess 25(OH)D exposure, as well as data from nearly 170,000 participants to evaluate spontaneous abortion outcomes.

The MR analysis indicated a potential association with a protective effect of higher 25(OH)D levels against spontaneous abortion, with odds ratios (ORs) as follows: inverse-variance weighted method (OR = 0.98, 95% confidence interval [CI] = 0.90–1.06), MR Egger (OR = 0.94, 95% CI = 0.84–1.05), weighted median (OR = 0.93, 95% CI = 0.82–1.06), and weighted mode (OR = 0.93, 95% CI = 0.84–1.03). However, these findings did not reach statistical significance.

To validate these results, a retrospective study was conducted with 60 pregnant women. The study found that median serum 25(OH)D levels were higher in women who had full-term deliveries compared to those who experienced spontaneous abortions (21.65 ng/mL, range = 19.63–25.40 vs. 19.80 ng/mL, range = 17.95–21.05), although this difference was not statistically significant (P = .053). There were no significant differences between the spontaneous abortion group and the term delivery group in terms of maternal age (29.25 ± 3.01 vs. 28.50 ± 2.77), gravidity (2 [1,3] vs. 2 [1,3]), and parity (1 [0,1] vs. 1 [0,1]).

Sensitivity analyses, such as the MR pleiotropy residual sum and outlier test, heterogeneity test, and leave-one-out analysis, supported the consistency of the results, although the P-values were not statistically significant.

The study authors concluded, "This study reports the potential protective role of [25(OH)D] concentration to abortion, that is, higher Vitamin D levels can decrease risk of abortion. Further larger prospective studies and/or even randomized controlled trials are needed to confirm causal relationship between vitamin D and [spontaneous] abortion."

The authors reported no conflict of interest.