Research published in Human Reproduction demonstrates that the likelihood of having multiple pregnancies after a single embryo transfer is smaller when compared with cases in which more than a single embryo is transferred.
Prof Peter Braude, Emeritus Professor of Obstetrics and Gynaecology, King’s College London (KCL), said:
“This is important data as it is the first time that the occurrence of twins (or more) after replacing a single embryo can be properly explained and the large data set allows the analysis to have some real clinical meaning that might require a rethink in practice. The fact that the multiple pregnancy rate is only 1.6% is reassuring, although there are risks when embryo splitting occurs.
“The data has allowed the authors to distinguish with reasonable certainty when there is only one sac and two embryos (monozygotic twins – worse outcome 71% live birth) from when there are two embryos in two sacs and a lower risk (81% livebirth), although both are still higher risk than when there is only one embryo in one sac (singleton pregnancy) – facts that were known but with less certainty. Although it is seems a matter of timing as to when the embryo splits, it is interesting that the occurrence of each type is roughly equal 51.2 vs 48.8%. Factors that they found may be associated with an increased risk of spontaneous embryo splitting after single embryo transfer were blastocyst culture, assisted hatching and thawed frozen transfers.
“We now have good data to be able to tell couples the likely risk of having multiple pregnancy after single embryo transfer, and that it is reassuringly small when compared to the huge number of multiples after two (or more) embryo transfer. Also the risk of splitting occurs in two embryo transfer too, but now all the attendant risks are added there being another baby in the uterus as well!
“It’s a useful and seminal paper mainly because of the size of the single embryo transfer data set – nearly a million SET cycles (937,848) producing over a quarter of a million clinical pregnancies (276,934) over a 7 year period. Big data makes a big difference.”
‘Prevalence and risk factors of zygotic splitting after 937 848 single embryo transfer cycles’ by Y. Ikemoto et al. WAS published in Human Reproduction at 00:05 UK time on Tuesday 9 October.
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