In in vitro fertilization (IVF), a woman is frequently given medications to encourage her ovaries to produce more than one egg at a time. In most cases, all of the eggs collected are fertilized with sperm. If any of the fertilized eggs develop into embryos, they are observed. The embryos are then returned to her uterus, one or more at a time. When numerous embryos are available, an elective Single embryo transfer (eSET) is when a person undergoing IVF decides to have a single embryo transplanted.
Previously, it was a common procedure to transfer multiple embryos at once during in vitro fertilization (IVF). This is because, prior to the introduction of new technology, transferring many embryos resulted in a greater pregnancy rate. However, those greater rates came with a danger of having twins, triplets, or higher-order pregnancies (multiple gestations), which put both mothers and kids at risk. When only one embryo is transferred, today's pregnancy rates are relatively high, but the danger of multiple gestations is considerably lowered with Single Embryo Transfer.
Development and improvements of embryo cryopreservation techniques has allowed supernumerary embryos to be retained and utilized in subsequent cycles if the first cycle is unsuccessful. A study included 331 women less than 36 years of age, with two good-quality embryos during their first IVF attempt. Subjects were randomized to either single- embryo transfer followed by single frozen-and-thawed embryo transfer (assuming no live birth) or to double embryo transfer. They found no statistically significant difference in live birth rate when comparing cumulative single embryo versus double embryo transfer rate (38.8 % vs. 42.9 %, P = 0.3). Compared to the SET arm, the rate of multiple births was significantly greater in the double embryo group (0.8 % vs. 33.1 %, P < 0.001). Over the last decade both observational and randomized studies have consistently observed similar rates of live birth rates in SET compared to DET, with a significant reduction in twin pregnancy rates with SET.
With extension of the duration of embryo culture from 2 to 3 days to 5 days (blastocyst stage) embryo(s) with the highest implantation potential may be selected for transfer. Improvements in implantation rates were observed and single blastocyst transfers were found to have superior pregnancy rates compared to single or double cleavage stage (day 2 or 3) transfer. Single day 5 blastocyst transfer was found to have similar live birth rates as those with two blastocysts transferred, and only half the multiple gestation rate. High quality blastocysts (defined by the 2010 Society for Assisted Reproductive Technology (SART) grading system based on morphology, expansion and overall quality) resulted in
significantly higher rates of live birth compared to use of lesser quality embryos.
Since IVF pregnancy rates continue to improve to their highest historical levels, there has been a significant emphasis on infant/perinatal outcomes and ART safety. Prior to the initiation of SET, 30 % of IVF cycles resulted in multiple gestations compared to the population rate of 1.5 %. Severe maternal complications include increased rates of anemia, hypertensive disorders and pre-eclampsia, gestational diabetes, postpartum hemorrhage, and operative deliveries. The European Society of Human Reproduction and Embryology Capri Workshop in 2000 addressed the 4 to 10-fold increase in perinatal morbidity and mortality associated with twins. Multiple gestations are at increased risk of preterm delivery (particularly early preterm <32 weeks or peri-viable delivery), fetal growth restriction and intrauterine fetal demise of one or both twins. Long term morbidity also includes complications from hypoxic ischemic encephalopathy and cognitive delays.
Emerging evidence has demonstrated the long-term neonatal benefits for infants conceived with SET. In a meta-analysis of studies between 1999 and 2010 which reviewed perinatal and neonatal outcomes in SET and DET, the risk of preterm birth and low birth weight was minimized with eSET. However, no significant difference were appreciated in the rates of spontaneous abortion, early preterm birth, or perinatal mortality. In a review of national data submitted to the Centers for Disease Control (CDC) from 1999 to 2010, patients who underwent single embryo transfer were twice as likely to have a good perinatal outcome when compared to those with more embryos transferred. The strongest predictor for a good perinatal outcome was utilization of elective single blastocyst transfer. Analysis of the 2011 CDC data showed women with favorable prognoses (defined as having at least one embryo more
available for cryopreservation) who underwent SET, had a significant increase in term healthy neonates and 77 % reduction in preterm births [9]. These findings suggest that the benefit of single embryo transfer extends beyond preventing multiple pregnancies. Moreover, recent studies have redefined the most relevant definition of IVF success as term gestation singleton live birth.
All patients with a chromosomally normal embryo identified through CCS, as well as the majority of egg donation recipients, have the option of undergoing eSET. Experts recommend restricting the transfer of euploid embryos to 1 in patients of any age who have a favorable prognosis to effectively reduce the number of multiple pregnancies and ensure the birth of one kid at a time. Consult your physician to see if Single Embryo Transfer is right for you.