How Many Embryos Should You Transfer?


You’ve completed your retrieval, your eggs have been fertilized, and you’re ready for an embryo transfer. Now you’re wondering, do we transfer one embryo or two? What is the difference in success rates? Is one option better than the other? Is there a risk with IVF twins?

Who should consider an elective single embryo transfer (eSET)?

All patients should consider having a single embryo transfer in an attempt to have one healthy baby at a time for both the safety of the mother and child. Multiple gestations can cause health issues for the mother (high blood pressure, diabetes, need for a cesarean section and delivery complications) as well as complications for the babies (preterm delivery, low birth weight, delayed lung development, neurological issues). As a result, the American Society for Reproductive Medicine (ASRM) and Society for Assisted Reproductive Technology (SART) revised their recommendations regarding the number of embryos to transfer in 2014 in an effort to promote singleton gestations and reduce the number of multiple pregnancies.

The ASRM recommendations are based on embryo quality, which accounts for several characteristics:

  • Embryo Developmental Stage: embryos on day 3 of development (cleavage stage) or embryos on day 5 of development (blastocyst stage)
  • Euploid Embryo: an embryo with a normal chromosomal complement based on pre-implantation genetic testing for aneuploidy (PGT-A).
  • Favorable Prognosis: a patient with a euploid embryo or one or more high quality embryos (based on appearance) or a patient with a history of a live birth from an IVF cycle.

The ASRM recommends that all patients, regardless of age, who have a euploid embryo have an eSET because PGT-A has been shown to increase the likelihood of implantation and live birth while reducing the chance of miscarriage. Patients under the age of 38 who have a “favorable prognosis” are also recommended to undergo a single embryo transfer, regardless of embryo stage or screening with PGT-A.

Additionally, a woman’s overall health is an important consideration in determining how many embryos to transfer. Women with pre-existing conditions that may be dangerous in the setting of a multiple pregnancy should not have more than one embryo transferred at a time.

What is the difference in success rates between a single embryo transfer and transferring multiple embryos?

Two embryos are not always better than one! In fact, the BEST trial in 2013 showed that the likelihood of success with a single embryo transfer is equivalent to that of a double embryo transfer (60.7% vs 65.1%) and that the risk of having a multiple gestation following a double embryo transfer is significantly increased (53% vs. 0%) compared to a single embryo transfer. Therefore, a single embryo transfer should strongly be considered for all patients before transfer of multiple embryos.

All patients considering transfer of multiple embryos should have a conversation with their doctor regarding their optimal plan of care and the additional risk of having twins or a higher order multiple pregnancy.

If you’re faced with the decision on how many embryos to transfer, weigh the pros and cons, pay attention to your instincts, and listen to your doctor.

Dr. Taraneh Gharib Nazem is Senior Fellow in Reproductive Endocrinology and Infertility at the Icahn School of Medicine at Mount Sinai/Reproductive Medicine Associates of New York. She is a board-certified Obstetrician Gynecologist. Dr. Nazem completed her residency in Obstetrics and Gynecology at the New York University School of Medicine, where she was elected administrative chief resident and graduated with the Robert F. Porges Honor Resident Award, for outstanding performance.