The odds that a woman will give birth after a fertilized egg is artificially introduced into her uterus appear to be much lower than fertility clinics tend to imply, according to a report in the 23 November issue of The Lancet. And women 35 years of age and older are the group most likely to be disappointed.
In one of the largest studies of its kind, a team led by Allan Templeton of the University of Aberdeen, U.K., analyzed records of more than 26,000 women who underwent in vitro fertilization (IVF) in the United Kingdom from 1991 to 1994. In the procedure, drugs stimulate the ovaries to produce eggs, which are withdrawn with a needle, fertilized in a lab dish, and injected into the uterus.
The Aberdeen group found that after their first IVF attempt, 25-year-old women had a 16% chance of giving birth, while the odds for 30-year-olds were only slightly better, at 17%. Success rates declined to 14% for 35-year-olds and plummeted sharply thereafter to 7% for 40-year-olds and 2% for 45-year-olds. The odds decrease with each unsuccessful IVF attempt, but if the procedure succeeds, the chances of a second success increase, Templeton says.
These findings contrast sharply with success rates claimed by some IVF clinics, which range as high as 40%. Part of the discrepancy lies in how fertility rates are computed, however. Sometimes there's "a degree of fudging," says Templeton. His team calculated success rates based on the number of live births per IVF procedure, while fertility clinics often judge success by the number of pregnancies achieved. Marsden Wagner, a reproductive consultant for the World Health Organization in Copenhagen, Denmark, says this different take on the numbers leads to unrealistic expectations.
The findings could cause insurance companies to reevaluate IVF coverage for women in certain age groups, says Templeton. "They may have to make a decision about whether to exclude certain patients because of low chances of success," he says.