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Elective Single Embryo Transfer Compared to Comprehesive Chromosomal Screening
A recent study by Reproductive Medicine Associates of Texas compared pregnancy rates of elective single embryo transfer with comprehensive chromosomal screening (CCS) in IVF patients 35 and under, compared to patients in the same age group who did elective single embryo transfer without CCS. The researchers concluded, “For the small percentage of cases that fit the criteria of having embryos available for transfer as well as cryopreservation, elective single embryo transfer without the additional cost of CCS may prove equally if not more beneficial.”
CCS is a type of preimplantation genetic screening (PGS), genetic testing that evaluates all 23 pairs of chromosomes in an embryo created in an IVF cycle. A "euploid" embryo has a correct number of chromosomes; an "aneuploid" embryo has an incorrect number of chromosomes.
A patient’s age and the number of embryos they create will give you a relative prognosis for the percent of embryos that is going to be euploid, says Dr. Ursula Balthazar, a fertility doctor with Reproductive Medicine Associates of Texas. In patients who are under 35 and have more than three embryos it is expected that at least half will be genetically normal. “So it makes sense that the implantation rate of those two patient populations is the same, but an impactful thing to have shown,” Balthazar says.
“At RMA, the patients who fall into the elective single embryo transfer group who do not have preimplantation genetic screening (PGS) are a very well counseled group. They meet criteria for elective single embryo transfer, meaning they have more than one embryo that qualifies for transfer on day 5,” she explains. One embryo is transferred and extra embryos are cryopreserved, or frozen. The study findings, "Make sense ultimately because it’s a good prognosis patient population, but it has helped us a lot in terms of counseling patients under 35 who are considering doing PGS.”
Patients have to understand the benefits and limitations of PGS, Balthazar says. It’s not just about the genetics of the embryo, she explains. “There’s a large focus within our field – we talk about the seed and the soil. You can have a seed that’s as tested as can be but ultimately the soil matters as well, and the environment of the combination of those two,” she says. “When you counsel patients, and they fully understand, their expectations are managed and that’s very helpful.”