For many couples, welcoming a healthy baby into their family is easy: They simply let nature take its course. For others, the journey is more difficult, and a healthy baby enters their lives only through the couple’s persistence and taking advantage of the latest scientific advances.
According to the most recent data from the Centers for Disease Control and Prevention, in 2018, nearly 81,500 babies were born as the result of assisted reproductive technology (ART). One of these technologies is in vitro fertilization (IVF), a method in which the woman’s eggs are harvested, fertilized in a laboratory, and then one or more embryos are transferred into her uterus. While this sounds straightforward, the heartbreaking truth is that only about four in 10 embryo transfers result in the birth of a baby.
For those pursuing ART, a viable pregnancy means beating those odds, and pre-implantation genetic testing (PGT) often can help. The goal of PGT is ensuring that the embryos transferred are those that have the best chance of growing into healthy babies. According to Wes Edmonds, PhD, scientific director of Assisted Reproductive Technologies at UAB Medicine, making that determination involves screening embryonic cells for genetic diseases and chromosomal disorders. “In simple terms, we perform a biopsy of the embryo,” Edmonds says.
From Fertilization to Biopsy
The initial stages of the PGT process are similar to in vitro fertilization. After the woman takes medications to stimulate egg production, her eggs are collected. “We attempt to fertilize all of them, but not all of the eggs will fertilize,” Dr. Edmonds says. The eggs that do fertilize are then allowed to grow for 5-7 days.
At that stage, the embryo has about 200 cells. The inner cells are those that would grow into a baby, while the outer cells would become the placenta – but both types of cells should be genetically identical. “We remove six to eight of the outer cells to test the genetic makeup of the embryo,” Dr. Edmonds says. “That way, we don’t interfere with the growth and development of the part that would become the baby.” UAB preserves the embryo through freezing while the cells are sent out for genetic testing.
When PGT Can Help
Pre-implantation genetic testing is available to every couple, though not every couple benefits equally. PGT is least likely to help women in their 20s and early 30s who aren’t facing fertility or pregnancy challenges.
“The odds are that their embryos are healthy at those young ages,” says William Hurd, MD, professor of Obstetrics & Gynecology at UAB Medicine. “Birth defects are uncommon, as embryos with genetic issues either never implant or the pregnancy ends in a miscarriage.”
Those most likely to benefit from PGT are:
- Women in their late 30s or early 40s: “The incidence of an embryo having an abnormal number of chromosomes increases in women of advanced maternal age,” Dr. Edmonds says. “A beautiful embryo can implant and have cardiac activity on an ultrasound but not have a chance of live birth.” Women carrying embryos with chromosomal abnormalities typically have miscarriages at 8-10 weeks. The PGT-A test looks for extra or missing chromosomes, so that the woman’s health care team can select embryos with the best chance of resulting in a successful pregnancy.
- Partners who have the same recessive gene mutation: “The PGT-M test can determine which embryos carry genetic abnormalities that the couple knows they have,” Dr. Hurd says. By selecting embryos that don’t carry the inherited mutation, there’s a reduced risk that a couple’s child would have, for example, Huntington’s disease or cystic fibrosis. “This opens the door to couples who might not otherwise choose to become parents,” Dr. Hurd adds.
- Women who have had multiple miscarriages: According to Dr. Hurd, there are several reasons why a woman might have miscarriages. “Half of the time the cause can’t be pinpointed,” he says. “For the remainder, miscarriages can have multiple causes, such as autoimmune disease, uterine abnormalities, or hormone problems.” The PGT-A test can find genetic abnormalities that prevent viable pregnancies, while the PGT-SR test can pinpoint more rare chromosomal issues called translocations or inversions. “All of the DNA is there, but in the process of cell division, it might have flipped into the wrong position,” Dr. Edmonds says.
- Parents who wish to balance their families: “PGT can determine the gender of an embryo, so parents can decide which embryo to transfer,” Dr. Edmonds says. “If parents want only one more child, gender choice can be important to them.”
The larger goals of PGT are to decrease the time to pregnancy, minimize the risk of a miscarriage, and maximize a couple’s opportunity to have a healthy baby. Achieving that goal comes down to numbers.
“If 10 eggs are harvested, on average, eight will be mature and appropriate to inseminate,” Dr. Edmonds says. “Of those eight, approximately six will become fertilized, and two or three of those will be able to be biopsied.” The goal is to find the healthy embryo that is the best candidate for transfer.
About four in 10 IVF patients at UAB Medicine choose to do PGT, and they face multiple decisions during their journey. UAB and other reproductive health care facilities across Alabama don’t have in-house genetic testing facilities, so the extracted embryonic cells are analyzed by an outside laboratory. The results are sent to the prospective parents and to their physician. Both their physician and the facility’s genetic counselor discuss the results and options with the couple.
“The genetic counselors know all of the scenarios and nuances,” Dr. Edmonds says. “They give excellent advice about the chances of success with individual embryos.”
If the results are complicated, the genetic counselors communicate the risk of transferring the embryos. “The partnership among UAB, the genetic counselor, and the couple is critical in ensuring the best possible outcome for our patient,” Dr. Edmonds says.
One difficult decision is whether or not to move forward with transferring a “mosaic” embryo, which are partially abnormal but may “self-correct” as they develop. “We talk about that upfront,” Dr. Hurd says. “There are some that we recommend transferring and some that we don’t.”
Dr. Edmonds emphasizes that UAB Medicine fully supports patient autonomy. “Once testing results are obtained, we may find that some of those embryos are mosaic or have genetic abnormalities that would not lead to a live birth,” he says. “Some patients decide to transfer these embryos in hopes that the genetic testing was incorrect.”
Embryos are watched carefully throughout their development, and only those that reach important milestones necessary for successful implantation and a healthy pregnancy are frozen. Some patients choose to limit the number of eggs that they fertilize, especially in cases where high numbers of eggs are retrieved. The extra eggs can be frozen for later use, and those that are fertilized will go on to develop into a smaller pool of embryos.
“The goal of an IVF cycle should be to create a single healthy child,” Dr. Edmonds says. “Having a couple of extra embryos in cryopreservation can be a plus for many patients who wish to further build their families.” However, in situations where patients have completed their family yet still have embryos remaining in cryopreservation, the ethical decision of how to handle the remaining embryos can be an emotional one.
While PGT may not benefit all prospective parents, it is available to everyone. Dr. Edmonds notes that UAB Medicine, as an academic medical center, is an equal opportunity provider.
“So long as the services requested fall within national guidelines for safe patient care, everybody deserves a chance,” Dr. Edmonds says. “PGT is a tool that can help some women shorten the time to a successful pregnancy, and we want to support them in their journey.”
Click here to learn more about infertility services at UAB Medicine.