The team of researchers examined the ovarian reserve in daughters using two methods: levels of anti-Müllerian hormone (AMH) and antral follicle count (AFC). They then used these numbers and compared them with the age of menopause in their mothers, finding that both AMH and AFC fall quicker in women whose mothers had an early menopause, in contrast to women whose mothers had a late menopause.
The number of eggs left in a woman's ovary is related to a decrease in her ability to conceive naturally, because as she ages the number and quality of her eggs begin to deteriorate.
Dr Janne Bentzen from the Copenhagen University Hospital, Rigshospitalet, in Copenhagen, Denmark, who led the research, said:
"This is the first study to suggest that the age-related decline of AMH and AFC may differ between those whose mothers entered menopause before the age of 45 years and those whose mothers entered menopause after the age of 55 years. Our findings support the idea that the ovarian reserve is influenced by hereditary factors.
However, long-term follow-up studies are required. Conclusive evidence can only be obtained when we have longitudinal studies that follow women who have AMH measurements over time until menopause. Therefore, interpretations of our data are limited and the findings we have described may not occur in any given individual."
Earlier studies showed that the period from when a woman's reproductive ability starts to drop until the beginning of the menopause is about twenty years. Therefore, a woman who begins to experience menopause at the age of 45, may have started a decline in fertility at age 25.
The link between the age at menopause among mothers and daughters has already been established. To confirm the belief of the 20-year period between the initial decline in fertility and the menopause, the authors suggested that maternal factors may also have an influence on a woman's reproductive ability, specifically in terms of ovarian reserve.
The investigators found 527 women who work in the health care field at Copenhagen University Hospital, ranging in age from 20 to 40 years and whose mothers' knew their age at the start of their menopause.
They were broken up into three groups:
- those who had an early menopause (before the age of 45)
- those with a normal maternal age at menopause (46 to 54 years)
- those with a late maternal age at menopause (older than 55 years)
AMH levels were calculated from blood samples. The researchers also documented a medical history, containing the mothers' and daughters' smoking habits, oral birth control use, and body mass index (BMI).
After adjusting for variance factors, the authors found that average levels of AMH declined by 8.6 percent, 6.8 percent, and 4.2 percent a year in the categories of daughters with mothers who had early, normal, or late menopauses, respectively. An similar sequence was seen for levels of AFC, with annual reductions of 5.8 percent, 4.7 percent, and 3.2 percent, in the same categories respectively.
The research also revealed that AMH levels and AFC were notably lower in oral birth control users than in non-users. AFC in women whose mothers smoked during pregnancy was 11 percent lower, however, there was no considerable effect on AMH levels.
The authors believe the effect of oral birth control use was probably temporary and not likely to impact the long-term reduction in ovarian follicles. They did note that women as well as healthcare professionals should be aware of this when taking into account a woman's reproductive life span and any fertility treatments.
The authors conclude:
"Clearly, our data do not elucidate whether maternal age at menopause is a direct predictor of age at menopause of the offspring, or the chance of pregnancy. Nevertheless, from a biological point of view, it may be reasonable to assume that a low ovarian reserve may have a long-term effect that will shorten the reproductive lifespan.
We therefore assume that markers such as 'maternal age at menopause' in combination with AMH or AFC, and chronological age may represent a more complete picture when evaluating the ovarian reserve of the individual. This assumption await longitudinal studies before it can be put to test."
Written by Kelly Fitzgerald