Fertility treatments such as in vitro fertilization (IVF) can be complex, oftentimes involving many decisions along the way. One of the toughest questions couples face is “How many embryos should we transfer?” This is an important question.
IVF is the process of stimulating the ovaries to produce multiple eggs, which are retrieved, fertilized with sperm, and result in embryos that are then transferred into the maternal uterus. Transferring more than one embryo at a time increases pregnancy rates, but it also increases the chances of multiple implantations leading to twins, triplets, etc.
In the early days of IVF, many of the laboratory and clinical techniques used with IVF were relatively new and unrefined. Therefore, the chance of achieving pregnancy per embryo transferred was low. Consequently, many clinics would routinely transfer multiple (2, 3, or even 4) embryos at a time in the hopes of achieving pregnancy at all. However, when pregnancy occurred with this approach, the result was often a multiple gestation pregnancy, which has a significantly higher chance of pregnancy complications including preterm delivery.
The technology associated with IVF has greatly advanced over the years. These advancements have led to a much higher chance of pregnancy per embryo transferred. The way embryos are cryopreserved (frozen) is far superior as well. This means that practitioners can now have excellent pregnancy rates while transferring relatively few embryos, preserving the additional embryos through cryopreservation for future pregnancy attempts. Consequently, the rates of triplet and quadruplet pregnancies have dramatically decreased over the past 10 years in the U.S. Because the transfer of two embryos is still a common practice, however, this has kept the chance of having twins with an IVF transfer averaging at about 30% nationally.
In 2009, to set standards on how many embryos should be transferred, the American Society for Reproductive Medicine (ASRM) published revised guidelines regarding the appropriate maximum number of embryos to transfer. These guidelines suggest a maximum number of embryos to transfer based on the day of transfer (Day 3 multi-cell embryos vs. Day 5 blastocyst), “prognosis category” (favorable vs. all others), and age of the patient. For most patients, these guidelines discourage the use of more than two blastocyst stage embryos in patients under the age of 40. Charts outlining the 2009 ASRM guidelines on the number of embryos to transfer can be found below: