A woman's fertility may be strongly linked to the age her mother was at menopause, according to research. Scientists estimate that women whose mothers went through the menopause earlier in life - before age 45 - are likely to have fewer eggs in their ovaries compared to women of the same age whose mothers had a late menopause.
Women are born with all the eggs they will ever produce and it is impossible to count how many eggs a woman has left in her ovaries, a measure known as 'ovarian reserve'. Instead, the researchers relied on accepted methods used by doctors to predict a woman's future fertility. These methods are sometimes referred to as the 'biological body clock test' and look at levels of anti-Mullerian hormone (AMH) in the women's blood and their antral follicle count (AFC).
In the study, published in the journal Human Reproduction, 527 women aged between 20 and 40, were divided into groups depending on whether their mothers had early, normal, or late menopause. Average levels of AMH declined by 8.6 percent, 6.8 percent, and 4.2 percent a year, respectively. Similar results were obtained using the groups' AFC readings.
'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', said lead researcher Dr Janne Bentzen, from the Copenhagen University Hospital in Denmark. 'Our findings support the idea that the ovarian reserve is influenced by hereditary factors'.
Other studies suggest there is about a 20 year gap between the time a woman's fertility starts to decline and the onset of menopause. This means women who enter menopause at 45 may have begun their decline in fertility from as early as 25 years old.
'In line with the suggested 20 years interval between the first decline in fertility and the menopause, we hypothesised that maternal factors may also have an impact on a woman's fertility potential', added Dr Bentzen.
However, other scientists have urged caution when interpreting the findings of the present study, as the ovarian reserve of individual women is subject to a large degree of variation. As a result, many women will have fewer eggs and yet still may not encounter problems becoming pregnant.
Dr Valentine Akande, consultant gynaecologist and spokesman for the British Fertility Society told the BBC: 'Whilst it is assumed that lower egg number is associated with more challenges at getting pregnant, this study did not look at that'.
The team behind the research is now planning a five-year follow-up study to better gauge an individual women's reproductive lifespan.