Factors associated with premature ovarian failure, early menopause and earlier onset of menopause in Japanese women.

Objective: The purpose of this study is to clarify the median age at natural menopause and the proportions of women with premature ovarian failure (POF) and early menopause (EM) by using Kaplan-Meier cumulative estimates and differences in reproductive and lifestyle factors associated with POF, EM and median age at menopause in a large population of Japanese women.

Subjects And Methods: This study is a cross-sectional analysis of the Japan Nurses' Health Study (JNHS). We analyzed data for 24,152 pre- and postmenopausal women who were 40 years or older at the JNHS baseline survey.

Results: The overall estimated median age at natural menopause was 52.1 years, and the proportions of women with POF and EM were 0.28% and 1.67%, respectively. Older generation, cigarette smoking, low body mass index, regular menstruation cycles at 18-22 years of age, nulliparity and unilateral oophorectomy were associated with earlier onset of natural menopause. Only unilateral oophorectomy was associated with increased risk of POF, and nulliparity and unilateral oophorectomy were associated with increased risk of EM.

Conclusion: Unilateral oophorectomy is a common factor associated with earlier onset of menopause, EM and POF, although other reproductive and lifestyle factors are not associated with POF or EM.