USC Fertility

How Many Embryos

How Many Embryos Should You Transfer?

Assisted Reproductive Technology (ART) has revolutionized the treatment of infertility and given millions of couples who had difficulty conceiving the chance to start a family. However, it has also introduced a significant increase in the number of “multiple pregnancies”, including twins and “higher order multiple” (HOM) pregnancies, consisting of three or more implanted embryos. There is overwhelming evidence that multiple pregnancies represent a major threat to the health of the mother and the fetuses. Most complications of pregnancy, such as pre-eclampsia, preterm labor and diabetes of pregnancy, are more common in multiple pregnancy compared to singletons, and the rate of babies born prematurely is much higher. Because of the increased risks to the mother and the infants, physicians try to prevent multiple pregnancy as much as possible. When higher-order multiple pregnancies occur, it is possible to reduce the risks for the mother and the fetus by performing a procedure called “multifetal pregnancy reduction”, whereby the pregnancy is reduced to a singleton or twin pregnancy under ultrasound guidance. However, despite a risk reduction achieved from this procedure, the risk to the pregnancy remains higher than the risk of a pregnancy starting out as a singleton or twin pregnancy. In addition, the procedure may result in inadvertent loss of the entire pregnancy, and even if this is not the case, the psychological consequences of facing this procedure are significant for any couple. For many couples, multifetal reduction is not option because of religious, cultural or personal reasons.

In view of this background, the American society for Reproductive Medicine (ASRM) and the Society for Assisted Reproductive Technology (SART) have issued guidelines for the number of embryos transferred in an IVF cycle. The recommendations for the number of transferred embryos are influenced by multiple factors, including patient age and embryo quality. The guidelines are not meant as strict rules but more as a help for patients and physicians- ASRM/SART state that “Strict limitations on the number of embryos transferred, as required by law in some countries, do not allow treatment plans to be individualized after careful consideration of each patients own unique circumstances.”However, every IVF program is asked to submit their statistics to a central database, and programs with an especially high multiple pregnancy rate may be subject to a SART audit.

When deciding on the number of embryos to transfer, clinicians consider what their patients’ prognosis for success. The prognosis is considered “favorable” if it is the first IVF cycle, the embryos are good quality (as determined by the embryologist monitoring them), and there are surplus embryos available for freezing. The prognosis is also considered “favorable” if the couple had a previous IVF success. It is important for the couple and their physician to have a good discussion about how many embryos to transfer so that the best outcome can be achieved after the couple makes an informed decision. The table below summarizes the ASRM / SART guidelines. It can be noted that in general, the recommendation is to transfer less embryos if the transfer occurs at the blastocyst stage (day 5-6 after fertilization) than if the transfer occurs at the cleavage stage (day 2-3 after fertilization). The reason for this is that if an embryo can reach the blastocyst stage in the laboratory it should have a higher chance of implanting.

It should also be noted that the number of transferred embryos goes up with age. Physicians can also increase the number of transferred embryos when previous IVF cycles were unsuccessful. In donor egg IVF cycles, the age of the donor is used to determine how many embryos should be transferred into the recipient. In frozen embryo transfer cycles, the “number of good quality embryos transferred should not exceed the recommended limit of fresh embryos for each age group.”