When undergoing in vitro fertilization (IVF), more and more couples are choosing to have their embryos screened to rule out certain disorders and even to select gender. According to Satin Patel, who specializes in reproductive endocrinology and infertility at North Texas IVF at Texas Health Presbyterian Hospital in Dallas, nearly half of his IVF patients are opting for preimplantation genetic screening, or PGS.
"The most common thing it's used for is screening, to pick up things like Down syndrome and abnormalities," Patel says. "The second most common thing we do it for is gender selection. That's very popular nowadays—for patients to want to choose the makeup of their family."
Patel says doctors can screen embryos five days after the egg and sperm combine in the lab. At that time, it's known as a blastocyst.
"We go all the way out to that stage because the embryo cells have begun to differentiate," he says.
By performing a biopsy on the cells, that become the placenta, he can conduct complex genetic screening on each embryo and determine whether the chromosomes are normal. In the past with IVF, it was common to implant more than one embryo, particularly in women who were older, because the odds were greater that an embryo was abnormal.
"As a woman ages, her eggs age, and genetic instances of problems increases dramatically," Patel says.
With PGS technology, however, doctors don't have to play a guessing game as to whether an embryo is normal. "You already know it's normal," Patel says. "So despite what age [the woman is], you can put back one normal embryo, and it's a safer option for patients."
Patel says PGS improves pregnancy rates and decreases incidences of multiple births. He adds that it has become much more common in recent years because the technology has improved and the price has become more affordable.
While PGS doesn't test for specific diseases, a more involved process called preimplantation genetic diagnosis (PGD) can pinpoint diseases, such as cystic fibrosis, Tay-sachs and Huntington disease. Patel says it's a more expensive procedure, and it's most often used by couples who know their child carries a risk for a disease because they already have a child who is affected.