In IVF success rates in American fertility clinics have improved, and the number of women having three or more babies in one pregnancy has decreased over the past ten years, a new study shows. The drop in multiple births following IVF treatment reflects a fall in the average number of embryos transferred following treatment, say researchers at Harvard Medical School in Boston. The group, who published their findings in the New England Journal of Medicine, say the most dramatic decrease occurred in 1997, after the American Society for Reproductive Medicine (ASRM) released guidelines for embryo transfer.
The researchers studied data on the outcomes of assisted reproduction technology (ART) procedures that were reported to the Centers for Disease Control and Prevention, between 1995 and 2001. They also looked at the incidence of twins, triplets and other multiple births, using data from the National Center for Health Statistics. They found that the average number of embryos transferred began decreasing in 1997, with the steepest drop (11.1 per cent) occurring between 1998 and 1999. In contrast, the number of pregnancies and births per cycle has gradually increased. And although the proportion of IVF twins born did not change much between 1997 and 2001, the percentage of pregnancies with three or more fetuses decreased every year, with a 20.8 per cent drop between 1998 and 1999.
In recognition of the health risks associated with multiple births, for both women and children, several countries have legislation that limits the number of embryos that can be transferred to the womb following IVF treatment. In the US, the decision is left to patients and their doctors but, in 1998, the ASRM published guidelines on the maximum number of embryos to transfer in different circumstances. It recommended that for women aged less than 35 years, those aged between 35-40 years and those over 40, the maximum number of embryos transferred should be three, four and five respectively. These guidelines were later amended, to say that no more than two embryos should be transferred in the treatment of women under 35, who have 'good quality' embryos, and enough to freeze for further attempts.
The researchers conclude that the voluntary guidelines are working, and federal law is not needed to control multiple births. In a commentary accompanying the paper, Robert Rebar of ASRM, and Alan DeCherney of the University of California, Los Angeles School of Medicine agree, saying that although the practice of ART is not legislated in the US, it is highly regulated. Regulation will continue to evolve as advances occur, they say, adding that 'there appears to be little justification for dramatic change or for additional legislation'.