Ovarian stimulation undertaken by women over 35 receiving fertility treatment may be leading to IVF failure, pregnancy loss or, more rarely, the birth of children with conditions such as Down’s syndrome, according to a new study.

Researchers believe that the procedure, which uses hormonal medication to prompt the ovaries to release a larger number of reproductive cells (oocytes) than normal, is disturbing a critical process of chromosome duplication called meiosis.

This leads to abnormalities of chromosome copy numbers resulting in adverse effects, they say.

Researchers will tell the annual conference of the European Society of Human Reproduction and Embryology in Stockholm, Sweden, today, that results of the research are leading to a new understanding about how such abnormalities are developing, and they believe that the ovarian stimulation a woman receives might be playing a part.

Alan Handyside, professor and director of The London Bridge Fertility, Gynaecology and Genetics Centre, in London, and colleagues from eight countries have been undertaking a study of a new way of screening polar bodies, small cells that are the by-product of oocyte development.

Prof. Handyside said: “We need to look further into the incidence and pattern of meiotic errors following different stimulation regimes including mild stimulation and natural cycle IVF, where one oocyte per cycle is removed, fertilised and transferred back to the woman.

“The results of such research should enable us to identify better clinical strategies to reduce the incidence of chromosome errors in older women undergoing IVF.”