Couples must not to leave it too late to try for a baby as it can lead to fertility problems in women, doctors have warned.
With more and more women pursuing careers, they and their partners are leaving parenthood to at least their late thirties.
But women aged 35 are six times more likely to have problems conceiving compared to those ten years younger, according to a major study from the Royal College of Obstetricians and Gynaecologists.
The report said older parents are making it harder for themselves to have children - and increasing the likelihood of serious medical complications for both mother and baby.
By the age of 40, a woman is more likely to have a miscarriage than give birth.
Men's fertility also declines rapidly from the age of 25 and the doctors estimate that the average 40-year-old takes two years to get his partner pregnant - even if she is in her twenties.
Up to 30 per cent of 35-year-olds take longer than a year to get pregnant, compared to only 5 per cent of 25-year-olds, according to the figures in the report by the Royal College.
Expectant mothers in their late thirties and forties are far more likely to suffer complications such as pre-eclampsia, ectopic pregnancy, miscarriage or stillbirth and they are also more likely to need a Caesarean.
Babies born to them are more likely to be premature, smaller or have Down's Syndrome and other genetic disorders.
"Clear facts on fertility need to be made available to women of all ages to remind them that the most secure age for childbearing remains 20-35," the Daily Mail quoted David Utting, specialty registrar in obstetrics and gynaecology at Kingston Hospital NHS Trust and co-author of the review, as saying.
The study has been published in the medical journal Obstetrician and Gynaecologist.