A woman breastfeeding her baby
Fertility peaks between 18 and 31 years of age, say experts
Women may be able to better gauge their own fertility based on the age their mother went through the menopause, a study has concluded.
Women whose mothers had an early menopause had far fewer eggs in their ovaries than those whose mothers had a later menopause, a Danish team found.
Women with fewer viable eggs have fewer chances to conceive, reports the BBC.
The study, of 527 women aged between 20 and 40, was reported in the journal Human Reproduction.
Researchers looked at two accepted methods to assess how many eggs the women had - known as their "ovarian reserve" - levels of anti-Mullerian hormone (AMH) and antral follicle count (AFC).
Women are born with all the eggs they will ever have. These are released from the ovary cyclically, usually one every month after puberty, until menopause.
The AFC and AMH give readings doctors an idea of how many yet-to-be released eggs remain in the ovary.
In the study of female healthcare workers, the researchers found both AMH and AFC declined faster in women whose mothers had an early menopause (before the age of 45) compared to women whose mothers had a late menopause (after the age of 55).
Average AMH levels declined by 8.6%, 6.8% and 4.2% a year in the groups of women with mothers who had early, normal or late menopauses, respectively.
A similar pattern was seen for AFC, with annual declines of 5.8%, 4.7% and 3.2% in the same groups, respectively.
Past research suggests there is about 20 years between a woman's fertility starting to decline and the onset of menopause. So a woman who enters the menopause at 45 may have experienced a decline in her fertility at the age of 25.
Lead researcher Dr Janne Bentzen said: "Our findings support the idea that the ovarian reserve is influenced by hereditary factors. However, long-term follow-up studies are required."
Also, having fewer eggs does not necessarily mean that the woman will go on to have fewer babies.
Dr Valentine Akande, a consultant gynaecologist and spokesman for the British Fertility Society, said the findings were helpful, but that women should not be overly concerned if their mother did have an early menopause.
"There is a huge amount of variation among women. Some will have more eggs and some will have less.
"Whilst it is assumed that lower egg number is associated with more challenges at getting pregnant this study did not look at that.
"Currently there is no test that can accurately predict fertility.
"The advice remains the same - the younger you start trying for a baby the more likely you are to be successful."
He said, in general, women are most fertile between the ages of 18 and 31.