Test-tube baby chances halved for over-35s

A woman's chance of a successful test-tube pregnancy drops sharply after the age of 35, according to a new analysis of more than 25,000 women treated in British clinics over three years.

The age of a woman is widely accepted as one of the most important factors influencing a successful outcome in in-vitro fertilisation (IVF). However, the new data derived from the Human Fertilisation and Embryology Authority's records since its inception in 1991 provides the best available evidence on the outcome of the treatment to date.

The overall success rate per IVF treatment was 14 per cent but it varied dramatically with age and was highest among women of 25 to 30. Surprisingly, women younger than this had lower success rates. The reason is not known and is under investigation. (It is already well-established that the "take home baby" rate varies widely between clinics, with some achieving success rates of up to 25 per cent.)

Professor Allan Templeton, of the Department of Obstetrics and Gynaecology at Aberdeen University, and colleagues calculated that about 16 per cent of women of 25 could expect to have a child, and 17 per cent of those aged 30.

But by 35 the success rate had fallen to 14 per cent per treatment cycle, and then fell steeply to 7 per cent by 40, and 2 per cent by 45. "No pregnancies were recorded in women older than 45 years," according to the report in today's issue of The Lancet.

Women who had previously been pregnant had a better chance of success than those who had never conceived, and this effect was stronger where there had been a live birth and strongest of all in those who had had a child by IVF.

The use of donor eggs, in place of eggs removed from the ovaries of the woman undergoing treatment, significantly improved the chances of success in women over 29 but diminished with age. This is thought to be due to the decreasing "receptivity" of the womb lining for a fertilised egg.

Professor Templeton said that the cause of infertility did not appear to influence the outcome but the chances of pregnancy fell with each failed cycle of treatment: "We found that the best possibility of success is in the first cycle of IVF treatment and that there is a significant negative effect with increasing number of attempts thereafter."

The live birth rate was better for women with unexplained infertility than for those in whom tubal disease (blockage, inflammation and so on of the Fallopian tubes) had been diagnosed.

Overall, 36,961 IVF cycles (70 per cent of all those registered between August 1991 and April 1994) in 26,389 women were investigated. Almost three-quarters of the women had one treatment cycle; one-fifth had two, and 8 per cent more than two. A further group of 1,416 IVF cycles using donated eggs were included in the study.