Single embryo transfer decreases the risk for multiple pregnancy without compromising IVF success rates.
When IVF protocols were originally designed back in the early 1980s, the goal was to obtain as many eggs (oocytes) as possible. This would ensure that the embryologists in the laboratory would eventually have several embryos available for transfer or freeze. This was necessary because successful conception was much more likely if more than one embryo was transferred at the same time. Part of the reasoning behind this strategy was to compensate for the known fact that 50% of human embryos have abnormal numbers of chromosomes within them. (This remains true whether fertilization takes place in the body or in the laboratory).
Over the years, as IVF techniques became more refined and the chances of successful conception greatly improved, the incidence of multiple gestations (twins, triplets, or more) began to climb precipitously. Multiple gestation is obviously a risky pregnancy for the mother but it is frankly dangerous for the babies. Many of the fetal risks are life-long or, in fact, life-threatening. Over the years, the number of embryos transferred per cycle has gone down but the multiple gestation rates remained unacceptably high.
Single embryo transfer (SET) reduces these risks enormously.
It’s impossible to identify which embryos are chromosomally normal simply by looking at them with a high-powered microscope. But, new technology now makes it possible to reliably check the chromosome numbers of an embryo before selection for transfer. This technique is called Pre-implantation Genetic Screening or PGS. Incorporation of this technique into IVF delivers the same chance of successful conception as would transfer of two or more embryos without incurring the risks of high order multiple gestations. The technique is also very useful for women who are at higher risk of having chromosomally abnormal embryos due to advanced maternal age. By avoiding unwitting transfer of abnormal embryos, the chance of miscarriage is greatly reduced.
Be sure to discuss PGS and SET with your physician if you are interested in optimizing your chances for a healthy and safe pregnancy via IVF.