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Trial Lecture – time and place
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Adjudication committee
- First opponent: Associate Professor Anna Sara Öberg, Karolinska Institutet
- Second opponent: Professor Ingvild Vistad, University of Bergen
- Third member and chair of the evaluation committee: Professor II Trond Melbye Michelsen, University of Oslo
Chair of the Defence
Professor Siri Vangen, University of Oslo
Principal Supervisor
Senior researcher Elisabeth Krefting Bjelland, Department of Obstetrics and Gynecology, Akershus University Hospital
Summary
The timing of menopause influences the length of the period when reproduction is possible, and also the risk of disease and early death. The aims of the thesis were to study if age at natural menopause has changed over time, to study if age at natural menopause increases by number of childbirths, and to study whether a successful spontaneous pregnancy is possible within 10 years before menopause. Data from > 300 000 women in the Norwegian breast cancer screening program (BreastScreen Norway) were used in two of the studies and data from > 4000 women in the HUNT2 Survey were used in one study.
We estimated a minor decrease in mean age at menarche, and an increase of approximately three years in mean age at menopause from the 1936 to the 1964 birth cohort. The mean age at natural menopause increased from 50.3 years among women born in 1936 to 52.7 years among women born in 1964. Thus, the mean number of years for reproduction increased by more than three years.
Women with three childbirths had the highest age at menopause and women with no childbirths had the lowest. Beyond three childbirths, we estimated no further increase in age at menopause.
We also found that more than 55 % of the women with early menopause gave birth within 10 years before menopause, whereas this was true for less than 1% of the women with late menopause. Almost no women gave birth after the age of 45 years.
The estimated increase in mean age at menopause may indicate an increase in the cumulative exposure to endogenous estrogens in the population, and could have attributed to the increased incidence in postmenopausal breast and endometrial cancers. As opposed to hormone related cancers, the risk of all-cause mortality seem to be reduced in women with high age at menopause. Thus, the increase in life expectancy for women in Norway the last decades could in part be explained by the increased age at menopause.
Additional information
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