The relation of number of childbirths with age at natural menopause: a population study of 310 147 women in Norway

Abstract

STUDY QUESTION Does age at natural menopause increase with increasing of number of childbirths? SUMMARY ANSWER Age at menopause increased with increasing number of childbirths up to three childbirths; however, we found no further increase in age at menopause beyond three childbirths. WHAT IS KNOWN ALREADY Pregnancies interrupt ovulation, and a high number of pregnancies have therefore been assumed to delay menopause. Previous studies have had insufficient statistical power to study women with a high number of childbirths. Thus, the shape of the association of number of childbirths with age at menopause remains unknown. STUDY DESIGN, SIZE, DURATION A retrospective population study of 310 147 women in Norway who were 50–69 years old at data collection. PARTICIPANTS/MATERIALS, SETTING, METHODS The data were obtained by two self-administered questionnaires completed by women attending BreastScreen Norway, a population-based screening program for breast cancer. The associations of number of childbirths with age at menopause were estimated as hazard ratios by applying Cox proportional hazard models, adjusting for the woman’s year of birth, cigarette smoking, educational level, country of birth, oral contraceptive use and body mass index. MAIN RESULTS AND THE ROLE OF CHANCE Women with three childbirths had the highest mean age at menopause (51.36 years; 95% CI: 51.33–51.40 years), and women with no childbirths had the lowest (50.55 years; 95% CI: 50.48–50.62 years). Thus, women with no childbirths had higher hazard ratio of reaching menopause compared to women with three childbirths (reference group) (adjusted hazard ratio, 1.24; 95% CI: 1.22–1.27). Beyond three childbirths, we estimated no further increase in age at menopause. These findings were confirmed in sub-analyses among (i) women who had never used hormonal intrauterine device and/or systemic menopausal hormonal therapy; (ii) women who were born before 1950 and (iii) women who were born in 1950 or after. LIMITATIONS, REASONS FOR CAUTION Information about age at menopause was based on self-reports. WIDER IMPLICATIONS OF THE FINDINGS If pregnancies truly delay menopause, one would expect that women with the highest number of childbirths had the highest age at menopause. Our results question the assumption that interrupted ovulation during pregnancy delays menopause. STUDY FUNDING/COMPETING INTEREST(S) This work was supported by the South-Eastern Norway Regional Health Authority [2016112 to M.S.G.] and by the Norwegian Cancer Society [6863294-2015 to E.K.B.]. The authors declare no conflicts of interest. TRIAL REGISTRATION NUMBER N/A.

Maternal age at birth of last child and cardiovascular disease mortality later in life among a national cohort of postmenopausal women from the United States

“…Although several studies have also observed this association, 42-45 others report no such relationship or an inverse association between late age at last childbirth and delayed onset of menopause 46 . Parity, however, has largely been reported to be positively associated with later onset of menopause 46-49 . Given that in the current study, women who had birth at later ages tended to have high parity suggests that childbirth at later ages may be a sign of delayed reproductive and somatic aging, and the fewer cumulative menstrual cycles that such parous women have due to multiple pregnancies may be associated with a larger reserve of oocytes and longer exposure to estrogen therefore delaying the onset of menopause 19,46 .…”

“…46 Parity, however, has largely been reported to be positively associated with later onset of menopause. [46][47][48][49] Given that in the current study, women who had birth at later ages tended to have high parity suggests that childbirth at later ages may be a sign of delayed reproductive and somatic aging, and the fewer cumulative menstrual cycles that such parous women have due to multiple pregnancies may be associated with a larger reserve of oocytes and longer exposure to estrogen therefore delaying the onset of menopause. 19,46 Thus, compared with primiparous women with childbirth at older ages, parous women with younger ages at first birth or nulliparous women, parous women with late age at last childbirth may have slower ovarian aging resulting in them benefiting longer from ovarian secretion of steroid hormones, including estrogen, progesterone, androgens, and various cytokines that affect the function of several reproductive organs, as well as other organs of the cardiovascular, musculoskeletal, and immune systems.…”

The dose–response relationship of pre-menopausal alcohol consumption with age at menopause: a population study of 280 497 women in Norway

“… 25 We identified year of birth (birth cohort), place of birth, number of childbirths, educational level, body mass index (BMI, kg/m 2 ) and smoking habits as possible confounders since these factors have been associated with alcohol consumption 26–29 and age at menopause. 1 , 30 , 31 Year of birth and BMI were included as continuous variables in the data analyses, whereas we treated place of birth (Norway, Europe, outside Europe), number of childbirths (0, 1, 2, ≥3), educational level (<high school, high school, <4 years of university, ≥4 years of university) and smoking habits (never smoker, former smoker, smoker) as categorical variables.…”

Aging conundrum: A perspective for ovarian aging

“…Subsequently, the rate of ovarian aging was unexpectedly accelerated. At the age of 51 years, the number of follicles decreased to 1000, which can be used as a threshold for menopause, as it corresponds to the average age of menopause in women (93,102).…”