Prospective evaluation of luteal phase length and natural fertility.

ObjectiveTo evaluate the impact of a short luteal phase on fecundity.DesignProspective time-to-pregnancy cohort study.SettingNot applicable.Patient(s)Women trying to conceive, ages 30-44 years, without known infertility.Intervention(s)Daily diaries, ovulation prediction testing, standardized pregnancy testing.Main outcome measure(s)Subsequent cycle fecundity.Result(s)Included in the analysis were 1,635 cycles from 284 women. A short luteal phase (≤11 days including the day of ovulation) occurred in 18% of observed cycles. Mean luteal phase length was 14 days. Significantly more women with a short luteal phase were smokers. After adjustment for age, women with a short luteal phase had 0.82 times the odds of pregnancy in the subsequent cycle immediately following the short luteal phase compared with women without a short luteal phase. Women with a short luteal length in the first observed cycle had significantly lower fertility after the first 6 months of pregnancy attempt, but at 12 months there was no significant difference in cumulative probability of pregnancy.Conclusion(s)Although an isolated cycle with a short luteal phase may negatively affect short-term fertility, incidence of infertility at 12 months was not significantly higher among these women.Clinical trial registration numberNCT01028365.