Plasma glycemic measures and fecundability in a Singapore preconception cohort study.

objectiveTo examine the association between plasma glycemia in women attempting to conceive and fecundability, as measured by time to pregnancy.

designProspective preconception population-based study.

settingHospital. PATIENT(S): Asian preconception women, 18-45 years old, attempting conception for ≤12 cycles at study entry. INTERVENTION(S): None. MAIN OUTCOME MEASURE(S): We ascertained time to pregnancy within a year of glycemic assessment in menstrual cycles. We estimated fecundability ratios (FRs) and 95% confidence intervals using discrete-time proportional hazards models, adjusting for age, ethnicity, education, body mass index, and cycle regularity and accounting for left truncation and right censoring. RESULT(S): We studied a population sample of 766 women from the Singapore Preconception Study of Long-Term Maternal and Child Outcomes prospective cohort. Compared with women with normoglycemia, women with dysglycemia (prediabetes and diabetes, defined by the American Diabetes Association) had a lower FR (0.56). Compared with the respective lowest quintiles, women in the highest quintile of fasting glucose (≥5.1 mmol/L) had an FR of 0.60, while women in the highest 2-hour postload glucose quintile (≥6.9 mmol/L) had an FR of 0.66. Overall, the FRs decreased generally across the range of fasting and 2-hour plasma glucose. Glycated hemoglobin was not associated with fecundability. CONCLUSION(S): Increasing preconception plasma glucose is associated with reduced fecundability, even within the normal range of glucose concentrations. CLINICAL TRIAL REGISTRATION NUMBER: NCT03531658.