Prospective evaluation of the impact of intermenstrual bleeding on natural fertility.

Objective: To evaluate the impact of an episode of intermenstrual bleeding on the probability of conception in a menstrual cycle (fecundability).

Design: Prospective, time-to-pregnancy cohort study.

Setting: Community-based cohort.

Patient(s): Women trying to conceive, ages 30 to 44 years, without known infertility.

Intervention(s): Not applicable.

Main Outcome Measure(s): Current cycle and subsequent cycle fecundability.

Result(s): A total of 549 women provided 1,552 complete cycles for analysis. Intermenstrual and luteal bleeding were reported in 36% and 34% of cycles, respectively. Ninety-three percent of all intermenstrual bleeding was luteal. Cycles in which women had intermenstrual bleeding or luteal bleeding were statistically significantly less likely to result in conception (fecundability ratio [FR] 0.23; 95% confidence interval [CI], 0.16-0.34; and FR 0.22; 95% CI, 0.14-0.33). Women with an episode of intermenstrual and luteal bleeding had a statistically significant increase in the probability of pregnancy in the subsequent cycle (FR 1.61; 95% CI, 1.15-2.25; and FR 2.01; 95% CI, 1.52-2.87, respectively).

Conclusion(s): Intermenstrual bleeding statistically significantly decreases the odds of conceiving in that cycle but does not appear to negatively impact a woman's immediate future reproductive potential.

Clinical Trial Registration Number: NCT01028365.