How Many Embryos Should We Transfer? Single Embryo Transfer (SET) versus Double Embryo Transfer (DET)

Many intended parents (IPs) going through in vitro fertilization (IVF) have more than one embryo available to transfer. Since the embryo transfer does not guarantee implantation, there can be a dilemma over how many embryos to use at a time. The decision whether to transfer on or more embryos is complex and personal.

In surrogacy, gestational carriers (GCs) and IPs often make this decision before the IVF cycle begins, even before legal contracts are complete. IPs may receive input from their clinic’s reproductive endocrinologist and embryologist to help in their decision-making. Due to the important nature of this topic, Heartland Surrogacy considers both a surrogate’s willingness to carry multiples and intended paretns’ desire to transfer multiple embryos during the matching process.

 

Pros of SET

The primary goal of a single embryo transfer is to reduce the risk of a multiple gestation pregnancy.  A single embryo transfer is the most likely scenario to grow one healthy baby at a time. (Remember, embryos can still split into identical twins during early pregnancy). Singleton pregnancies have lower risks for both carrier and baby, including lower risks of pregnancy complications, cesarean sections, and prematurity.

Some IVF patients wish to transfer more than one embryo in hopes that it will increase their chance of pregnancy. However, recent advancements in IVF technology have led to higher success rates, regardless of the number of embryos transferred. The increase in success rates is propelled by the prominence of using blastocysts (often called “Day 5/6” embryos) as well as the increased availability and affordability of embryo screening (PGS/PGD/CCS). In fact, recent studies determine that transferring one screened embryo has similar success rates to transferring two unscreened embryos.

According to the American Society of Reproductive Medicine (ASRM), one randomized control trial comparing SET and DET of blastocyst stage embryos demonstrated no statistical difference in pregnancy rates and a reduction in multiple gestation from 47% to 0%.

Additionally, embryo freezing and thawing techniques have also improved, so extra embryos may be transferred in later cycles. There is evidence from well-controlled nonrandomized trials and clinical reports that, if the contribution of subsequent cryopreserved embryo transfers are included, cumulative success rates are similar for SET and DET.

Because of these improvements in implantation rates, many IVF clinics now require a single embryo transfer if there are multiple blastocysts available, the egg provider is under age 35, and there are no previous IVF failures.

Cons of SET

Many couples pursuing IVF and surrogacy have already undergone a long and emotionally exhausting fertility journey. The IPs may be fatigued by this process and want to transfer more than one embryo at a time, hoping for a higher success rate, even if it increases the risk of multiples. In addition to the emotional cost of multiple transfers, there is a financial cost. Often times in the US, fertility treatment is not covered by insurance. Therefore, there are additional costs for each embryo transfer, in an already long and expensive journey.

Pros of DET

Embryologists may sometimes recommend a DET based on factors including the number of embryos, previous failed transfers, and the age of the person who provided the egg. For example, an embryologist may recommend a DET if utilizing Day 3 (cleavage stage) embryos, if the person who provided the eggs is over 35, or if there have been previous unsuccessful transfers.

Some IPs may prefer a DET because they want multiple children and would welcome a multiple gestation pregnancy. For example, two men may hope to have a set of twins that can each carry one of their genetic material. Some surrogates may already have experience with an uncomplicated twin pregnancy and may be comfortable with a DET and potential multiple gestation.

Cons of DET

Double embryo transfers are significantly more likely to result in multiples.  Multiple gestation rates after the transfer of two top-quality blastocysts are reported to be between 50% and 60%, and spontaneous triplet gestation rates are 2-5%. A multiple gestation pregnancy is often more expensive and has a higher rate of pregnancy complications for the carrier, including gestational diabetes, high blood pressure, and pre-eclampsia. Multiple births also have a higher rate of delivery complications, including various labor complications and cesarean sections.

According to the Centers for Disease Control (CDC), twins have a higher incidence of medical complications compared to singletons, including pre-term delivery (65% in twins, compared to 14% in singletons), low birth weight (57% vs. 9%) and very low birth weight (9% vs. 2%). These complications often lead to neonatal intensive care after birth, which may create extra challenges for international/out of town IPs. Multiples also have a higher rate of permanent, sometimes severe, disabilities, including long-term respiratory and gastrointestinal problems, vision issues, cerebral palsy, other neurological damage, and even death. Because of the potential complications, twins rarely result in the “two for one” cost some intended parents may hope for.

The decision of whether to utilize a single or double embryo transfer should not be taken lightly. An educated decision can be made after considering the risks, desire for multiple children, financial considerations, and the expected implantation rate. IPs and GCs should work together to come to a decision that they are both comfortable with, understanding that the recommendations may change as treatment progresses.