One of the biggest risks from infertility treatments, particularly assisted reproductive technologies like inseminations and in vitro fertilization is multiple pregnancy. The risk of twins can occur in up to 30% of pregnancies that result from assisted reproductive technologies. Multiple pregnancy is not always a desired outcome.
Twin pregnancies are generally safe and generally go very well. However, there is an increased risk as compared to single pregnancies of premature labor that can result in damage to the fetus, including to the fetal lungs, to the fetal eyes and to the fetal brain. Also, premature deliveries can result in significant immaturity of lung function, causing the baby to require a respirator at the time of birth.
It is important to minimize the risks of multiple pregnancy. There are many measures being taken by reproductive endocrinologists at this time to do just that. In vitro fertilization offers significant advantages over insemination in controlling multiple pregnancy. In insemination treatment, sperm is injected into the uterus and as many eggs as a woman has that are mature can potentially fertilize.
In in vitro fertilization, however, there's control because only the number of embryos transferred into the uterus by the physician can result in pregnancy. Even if we transferred two embryos into a woman at the time of embryo transfer, there's still approximately a two out of three chance or even higher that only one will take if pregnancy occurs.
However, we try to minimize the risks by being very careful about the number of embryos to transfer. In women who are younger, we transfer less embryos, even sometimes just a single embryo. In women who are older, however, it's often better to transfer more embryos than one because the chances of implantation per embryo diminish with age.
Should a twin pregnancy, a triple pregnancy or higher occur, selective reduction of fetuses can be achieved using a needle and potassium chloride solution. However, this process is often emotionally and physically difficult for couples and should be avoided by taking good care to consider the risks of multiple pregnancy in every therapy and being certain to know when to transfer more than one embryo.