Even though their menstrual cycle may appear normal after cancer treatment, the women may be able to produce fewer eggs than normal.

Experts are advising that such women should receive fertility counselling so that they are made fully aware that their reproductive life may be shortened.

Dr Elisabeth Larsen, from the Fertility Clinic at Copenhagen University Hospital, Denmark, studied 26 long-term survivors of acute lymphoblastic leukaemia (ALL).

They should not postpone childbearing, and it might be that they should consider becoming mothers before pursuing a career

Dr Elisabeth Larsen, Copenhagen University Hospital

She found that they tended to have smaller ovaries with fewer follicles (the group of cells containing the female egg) available in each menstrual cycle.

However, the good news was that their ovaries appeared to be functioning normally in all other respects, she told the annual conference of the European Society of Human Reproduction and Embryology.

Longer term effects

She said: "Multi-agent chemotherapy has radically increased long-term survival of children with acute lymphoblastic leukaemia, but the treatment can induce late effects.

"It is well known that a proportion of the patients experience ovarian failure and infertility.

"The new finding is that female childhood cancer survivors with an apparently normal menstrual cycle might have a shortened reproductive span."

Eight of the 26 women who took part in the study became pregnant naturally, resulting in 12 babies, one abortion and two ongoing pregnancies.

One woman, aged 33, had tried to become pregnant without success for five years, but many of the women were young and 17 of the 26 had not even tried to conceive yet.

Reassurance

Dr Larsen said: "Although these long-term survivors of childhood leukaemia have an apparently normal ovarian function, our results suggest that the chemotherapy has reduced the numbers of follicles in the ovaries.

"Therefore it is important that women who have survived childhood leukaemia should receive careful and individual fertility counselling as their reproductive life may be shortened."

She said that it was not possible to give a precise estimate of how much shorter the women's reproductive life might be.

However, she recommends that all female survivors of childhood cancer with normal ovarian function that they should try to have their first child before they are 30.

"The important message to come from this research is women who have survived ALL can become pregnant and have babies and they are doing so.

"However they should not postpone childbearing, and it might be that they should consider becoming mothers before pursuing a career."