Reproductive characteristics and risk of uterine leiomyomata.

OBJECTIVE

To evaluate whether menstrual and reproductive characteristics may influence development of uterine leiomyomata since sex steroid hormones have been hypothesized to play a role in their development.

DESIGN

A prospective cohort study (Nurses' Health Study II).

SETTING

Participants were identified from 14 states and followed for 14 years.

PATIENT(S): A cohort of 116,609 female registered nurses ages 25-42 at baseline.

INTERVENTION(S): We obtained data on uterine leiomyomata incidence and exposures through biennial questionnaires. We calculated hazard ratios and 95% confidence intervals adjusted for known and suspected risk factors.

MAIN OUTCOME MEASURE(S): Uterine leiomyomata confirmed by ultrasound or hysterectomy.

RESULT(S): During 1,163,439 person-years of follow-up, 9,847 self-reported cases of hysterectomy- or ultrasound-confirmed uterine leiomyomata were reported. We observed a lower incidence of uterine leiomyomata with later age at menarche, longer menstrual cycles, parity, later age at first and last birth, shorter time since last birth, and breastfeeding.

CONCLUSION(S): Hormonal and anatomical changes associated with menstruation and pregnancy may influence uterine leiomyomata incidence.