As fertility treatment continues to help more women/couples achieve their family building goals, we have continued to see the risk of twins decline. IVF has helped drive up fertility treatment while also helping reduce the risk of twins. That’s occurred mainly through efforts to encourage Elective Single Embryo Transfer (ESET). At our center, nearly 90% of our patients agree to ESET and we feel that this strategy has actually helped us achieve among the highest live birth rates attainable.
Even with ESET however, twin pregnancies do occur. That is primarily due to a single embryo splitting. In fact, sometimes an embryo can split and become a triplet pregnancy. Whenever an embryo splits; the resulting babies are genetically the same and therefore referred to as “identical twins.” Identical twins are naturally conceived in about 0.45% of pregnancies. Recently a large analysis of 7 years worth of data helped clarify the incidence of identical twin from embryo splitting in IVF.
Japan performs the highest number of IVF cycles per capita than any other nation. In Japan, they have shifted to single embryo transfer in about 80% of their treatment cycles. This recently made it possible for a group of researchers to review 937,848 single embryo transfer cycles to determine how frequently embryos appear to split following IVF. Their conclusions were as follows:
- The risk of multiple pregnancy after single embryo transfer is 1.60%
- This results in a risk of twins that is 1.56% following single embryo transfer
- The risk of triplets when one embryo is used is about 0.04%
- About 1.36% of embryos appear to split while the remaining number of multiples are believed to be a combination of natural conception along with single embryo transfer—this is the reason that we discourage intercourse following an embryo transfer.
- Embryos are more likely to split if they were created by eggs from younger women and those with unexplained infertility.
- Pregnancies resulting from embryo splitting are at higher risk of miscarriage
In summary, with today’s improved technology for freezing embryos, it is safest to transfer one embryo at a time to optimize live birth rate and reduce the risk of multiple pregnancy.