Preconception vitamin D and miscarriage in a prospective cohort study

Is preconception vitamin D level associated with the risk of miscarriage? Preconception vitamin D levels are not associated with the risk of miscarriage in a population of women conceiving naturally. In humans, low vitamin D has been associated with prolonged menstrual cycles, delayed ovulation and a lower probability of conception. Animal and in vitro data indicate that vitamin D may affect implantation. This prospective time-to-pregnancy study included 362 women who were trying to conceive naturally between 2008 and 2015. This study included participants who had been trying to conceive naturally for 3 months or less at enrollment and aged 30-44 years. A preconception blood sample was collected and 25-hydroxyvitamin D [25(OH)D] was measured. Women who conceived (N = 362) were at risk of a miscarriage from the day of a reported positive pregnancy test until either a participant-reported pregnancy loss or 20 weeks post day of last menstrual period, whichever came first. Gestational age was defined by ovulation. Time to miscarriage (days) or censoring was modeled using a multivariate Cox proportional hazards model. Multiple imputation was performed for missing covariates and missing day of ovulation. The mean age was 33 years (SD: 3.0 years). Mean 25(OH)D was lower among those who reported their race as African-American and those with a higher BMI. After adjustment for age, race, BMI, education, exercise, alcohol and caffeine intake, compared to the referent group (30-