The process of IVF involves an investment of time, emotional stress, and expense. When a couple has gone through this process, they would like to ensure that they have the best chance possible of reaching their goal of having a baby. However, the goal of IVF is to help the couple have a single baby, though we recognize that twin pregnancies are not uncommonly the outcome. Ideally, each embryo would produce a live born baby, but unfortunately, this is not the case. Many factors may affect an embryo’s ability to continue to grow normally. Because of this fact, often more than a single embryo is transferred back to the uterus.
The decision on how many embryos to transfer is a difficult one that tries to reach a balance between having a pregnancy and ultimately a live birth, but not having a multiple pregnancy. This decision is a joint plan between both the couple and the physician, and is reached only after a thorough discussion of the many critical aspects involved.
Embryo transfers most commonly occur on the third day (cleavage stage) or fifth day (blastocyst stage) following egg retrieval. Ideally, embryo transfer would always occur at the blastocyst stage, as these embryos have a higher success rate, which can allow for the transfer of fewer embryos, thereby giving a higher pregnancy rate while limiting the number of multiple pregnancies. Unfortunately, not all patients will have enough high quality embryos to make it to the 5th day for transfer. In these patients, we often feel that transferring the embryos on the 3rd day will provide a reasonable pregnancy rate in those situations in which extended culture would not have provided an adequate number of surviving blastocysts.
Factors that should be considered are many, including the age of the woman (or the egg donor), previous reproductive outcome, previous IVF outcome, quality of the embryos, day of transfer, the couple’s reproductive goals, patient body habitus, and any co-existing complicating medical conditions.
The ASRM (American Society for Reproductive Medicine) has published guidelines on the recommended number of embryos to transfer.
Though not legally required, it is strongly suggested that deviations from these numbers only occur in certain circumstances.
More recent data is being published demonstrating the benefits of transferring only a single good quality blastocyst. This should be considered in the under 35 group with a favorable outcome, and more especially for those under 30. Single embryo transfer can give very satisfactory pregnancy rates, while maintaining very low rates of twins (<3%). This is compared to the twin rate by transferring two blastocysts, which can be 25-30%, with a ~4% rate of triplets (if one embryo should split on its own).
In summary, the decision on the number of embryos to transfer must be made between the patients and physician taking into account many different factors, and should be undertaken after thorough consideration of the risks involved.