The greatest risk element in any form of assisted conception, is the risk to a fetus within a multiple pregnancy, even with twin implantation. Recent research has examined the contribution of single embryo transfer in reducing the incidence of multiple gestation within IVF. Two recent studies from our assisted conception centres have demonstrated that single embryo transfer can be undertaken without compromising the patient’s ultimate chance of having a successful ongoing pregnancy. The first study was a randomized trial comparing the pregnancy rates in women having two embryos transferred at day two or three after oocyte collection, with that of a second group undergoing single blastocyst transfer. The results revealed an
equivalent ongoing pregnancy rate but a significant reduction in the twin rate (to zero) in the single transfer group. A second study examined the cumulative pregnancy rate in women with two or more suitable blastocysts after oocyte collection for transfer, when the final chance of pregnancy was calculated after all embryos had been transferred fresh and in subsequent frozen-thaw embryo transfers. The results were calculated for
two groups of women in this data set, one receiving a single embryo for transfer fresh and the second group having two embryos transferred fresh. There was an initial improvement in the fresh embryo transfer group having two transferred (59% vs 44% for the single transfer group), but when additional pregnancies from frozen-thawed pregnancies were added, there was no difference in the final cumulative pregnancy rate in either group (74% for the single transfer group and 70% for the double transfer group). In contrast, 28% of overall pregnancies in the (initial) double transfer group were multiple, whereas only 5% of the (initial) single transfer group were twins. The development of high quality incubation systems within IVF that allow for both blastocyst culture and successful cryopreservation allow for both a high pregnancy rate and the development of strategies to reduce the multiple pregnancy rate.

Keywords: Multiple pregnancy, ART