Researchers used ultrasound to count the number of follicles each woman had in the study. (Cheryl Ravelo/Reuters)

A mother's age at menopause may predict when her daughter’s fertility declines, a new study suggests.

Population studies suggest an association between the age of menopause among mothers and daughters. Now researchers have used hormone levels and counts of eggs remaining in ovaries to estimate how fertility may relate to mother’s age of menopause.

"To our knowledge, this was the first study to demonstrate a significant association between age at maternal menopause and serum anti-Mullerian hormone levels in daughters," Dr. Janne Bentzen from the Copenhagen University Hospital in Denmark and co-authors concluded in Tuesday's issue of the journal Human Reproduction.

The findings suggest that age-related declines in the hormone and follicles differs between those whose mothers entered menopause before age 45 and those whose mothers started after 55, Bentzen added in a release.

In the study, 527 women working in health care at Copenhagen University Hospital who were aged 20 to 40 were divided into three categories:

• Those whose mothers had an early menopause at younger than 45.
• Normal maternal age at menopause of 46 to 54.
• Late maternal age at menopause of older than 55.

An investigator who was unaware of the women' hormone profiles and questionnaire answers did the clinical exam. They used transvaginal ultrasound to count the number of follicles — clusters of cells that contain the immature egg.

Average levels of the hormone in blood declined by 8.6 per cent, 6.8 per cent and 4.2 per cent a year in the groups of women with mothers who had early, normal or late menopauses, the researchers found.

The follicle counts showed a similar pattern of decline of 5.8 per cent, 4.7 per cent and 3.2 per cent.

Factors like smoking, use of contraceptive, age and body mass index were considered in the analysis.

Both the hormone levels and follicle counts were lower (27.3 per cent and 26.8 per cent lower) among oral contraceptive users, an effect that Bentzen said was likely temporary but one that doctors and women should be aware of when considering their reproductive life spans or fertility treatments.

Women participating in the study all worked in the health-care field who might have been healthier than the general population.

The researchers called for longer-term follow-up studies to estimate hormone and follicle levels at an individual level. They are planning a five-year study.

The research was funded by the Danish Agency for Science, Technology and Innovation, the Copenhagen Graduate School of Health Science and the Fertility Clinic at Copenhagen University Hospital.