Low-dose aspirin in reproductive health: effects on menstrual cycle characteristics.

Objective: To estimate the effect of daily 81 mg low-dose aspirin (LDA) on menstrual cycle length and hormone profiles.

Design: Secondary analysis of a trial evaluating the effect of daily LDA or placebo on live birth among women with one or two previous pregnancy losses.

Setting: University medical centers.

Patient(s): A total of 915 regularly menstruating women who had at least one menstrual cycle (3,190 total cycles) in which pregnancy did not occur.

Intervention(s): Randomized allocation to LDA versus placebo.

Main Outcome Measure(s): Menstrual cycle length and follicular and luteal phases were measured. Urinary pregnanediol glucuronide, follicle-stimulating hormone, luteinizing hormone, and estrone-3-glucuronide were assessed up to six times during the first two cycles. Generalized estimating equations estimated relative risk of short (<25th percentile: <27 days) and long (>75th percentile: ≥32 days) versus normal cycle length. Linear mixed models estimated mean hormone level differences with weights used to account for multiple cycles contributed per participant.

Result(s): There were no significant differences in total menstrual cycle, follicular phase, or luteal phase length between LDA and placebo groups. LDA posed no greater risk of having a short versus normal-length or long versus normal-length follicular phase, or having a short versus normal-length or long versus normal-length luteal phase. There were no significant differences in hormone levels across the menstrual cycle between the LDA and placebo groups.

Conclusion(s): Daily LDA use did not result in any changes to menstrual cycle, follicular phase, or luteal phase length or hormone levels across the menstrual cycle compared with placebo.

Clinical Trial Registration Number: NCT00467363.