95% CI ¼ 1.01, 2.05, versus %1.95 ng/mL RR ¼ 1.08; 95% CI ¼ 0.81, 1.43), a marker of systemic low-grade inflammation. In analyses utilizing available karyotype data from clinical pregnancy losses, sufficient versus insufficient vitamin D was also positively associated with pregnancy with a male fetus (RR ¼ 1.21; 95% CI ¼ 1.01, 1.46). Estimates were stronger among women with high versus low levels of hsCRP (>1.95 ng/mL: RR ¼ 1.34; 95% CI ¼ 0.96, 1.88 versus %1.95 ng/mL RR ¼ 1.12; 95% CI ¼ 0.90, 1.39), though not statistically significant.CONCLUSIONS: Our findings that preconception vitamin D status is positively associated with male live birth and pregnancy with a male fetus, particularly among women with elevated inflammation, suggest that sufficient levels of preconception vitamin D may mitigate maternal inflammation that would otherwise be detrimental to the implantation or survival of male conceptuses in utero. These findings highlight the importance of vitamin D in reproduction and implicate a novel factor associated with altered offspring sex ratio in humans.

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