Chances of live birth after exposure to vitamin D-fortified margarine in women with fertility problems: results from a Danish population-based cohort study

Objective: To study the association between extra vitamin D from a mandatory margarine fortification program and chance of live birth among infertile women. Design: Nationwide cohort study. Setting: Not applicable. Patient(s): The study population consisted of 16,212 women diagnosed with infertility from June 1, 1980, to August 31, 1991. Interventions(s): We took advantage of the mandatory vitamin D fortification program of margarine in Denmark that was abruptly stopped on May 31, 1985. The termination of the vitamin D fortification served as a cutoff point to separate the study population into various exposure groups. Main Outcome Measure(s): Odds ratios and 95% confidence intervals for the association between vitamin D exposure status and chance of a live birth within 12, 15, and 18 months after first infertility diagnosis. Result(s): Women who were diagnosed with infertility during the vitamin D-exposed period had an increased chance of a live birth compared with women diagnosed with infertility during the nonexposed period. For women diagnosed with infertility during the washout period, the chance of a live birth was also increased, but somewhat lower. Similar estimates were obtained with longer follow-up, in women with anovulatory infertility, and little seasonal variation was observed when calendar period of conception was applied. Conclusion(s): Our findings suggest that infertile women exposed to extra vitamin D from a margarine fortification program had an increased chance of live birth compared with women not exposed to extra vitamin D from fortification. (C) 2019 by American Society for Reproductive Medicine.