Mandish Dhanjal, a consultant obstetrician, said that the example of celebrity older mothers, such as Madonna and Holly Hunter, gave women the wrong impression about the ease of motherhood at an older age.
Mr Dhanjal, who has collated the evidence on the medical risks faced by older mothers for a report for the College, said: "Many young women will be reading magazines which focus on this. Unfortunately the mass media doesn't tend to report the complications."
Although still relatively small, the risk of medical complications in pregnancy is between two and five times higher in women in their 40s than those in their 20s.
These can include diabetes in pregnancy and pre-eclampsia, which can cause serious problems for both mother and baby.
Fertility also declines rapidly after the age of 35, making it much harder to become pregnant, the report will warn.
Yet there is a growing trend for women to put off becoming a mother.
Mr Dhanjal said: "If you look at older mothers over the age of 35 - in the mid 1980s about 8 per cent of those women who got pregnant were over 40 whereas now that figure has more than doubled to 19 per cent."
The college commissioned the report after figures showed that the number of older mothers had risen to record levels.
In 2008 there were 26,419 births to women over the age of 40.
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