Transferring a single blastocyst has been shown to significantly reduce multiple pregnancy rates and to increase the likelihood of delivering at term a single healthy baby. There is an acceptance that the incidence of monozygotic twin births is higher in the ART population compared with naturally conceived births. However, there are conflicting reports regarding treatment methods in ART and their involvement in increasing the twinning rate. The objective of this study was to use gender discordance to estimate the monozygotic and dizygotic twinning rates following the transfer of single fresh or frozen embryo. A retrospective cohort analysis of 4,701 fresh and frozen IVF/ICSI treatment cycles was conducted. There was no difference in the twinning rate whether fresh or frozen embryos were used in either IVF or ICSI procedure. At least three quarters of twin births following a SET in a frozen cycle were discordant presumably due to a concurrent naturally conceived pregnancy. Patients should be advised to avoid intercourse prior to FET as twin pregnancy has a higher degree of risk and complication.
The results for this project were presented at the Fertility Society of Australia annual scientific meeting 2013 and were published in the journal Human Reproduction in 2014.
Reference: Osianlis T, Rombauts L, Gabbe M, Motteram C, Vollenhoven V. Incidence and zygosity of twin births following transfers using a single fresh or frozen embryo. Hum Reprod. 2014 Jul;29(7):1438-43.