A practice committee opinion released at the annual meeting of the American Society for Reproductive Medicine (ASRM) on October 16 concluded that evidence does not support the use of preimplantation genetic screening (PGS) for any indication. The release of the opinion, which surprised many at the meeting, spurred vigorous debate and a dissenting public statement by the Preimplantation Genetic Diagnosis International Society (PGDIS).

PGS and preimplantation genetic diagnosis (PGD) both begin with in vitro fertilization (IVF): eggs and sperm are collected from would-be parents, and fertilization takes place in the lab. After a few days, one or two cells are taken from each of the resulting embryos for analysis. In PGD the embryos are tested for a genetic disease for which the future child is known to be at risk. PGS, by contrast, seeks to identify embryos with chromosomal abnormalities – a condition known as aneuploidy. Down syndrome is a result of one type of aneuploidy, but the majority of aneuploid embryos result in failed pregnancies. In fact, aneuploidy is the most common cause of early miscarriage, making it a seemingly logical target for IVF clinics trying to increase success rates.

The controversy over PGS centers on whether it works in practice – that is, whether screening embryos for aneuploidy increases the chances of a healthy birth. Some studies support the use of PGS, particularly for patients experiencing recurrent miscarriages. However, one recent randomized, controlled study found that PGS did not improve pregnancy or live-birth rates among women of advanced maternal age, and may in fact be detrimental. In general few data have been collected or made available on the practice of PGS in the United States – how often it is performed, for what indications, and with what outcomes. Despite conflicting studies and uncertainty about its safety and efficacy, demand for and availability of PGS are widespread.

The ASRM practice committee opinion summarizes the results of studies of PGS for four indications: advanced maternal age, recurrent pregnancy loss, repeated implantation failure, and male factor infertility. In each case, the committee found that “available evidence does not support the use of PGS as currently performed to improve live-birth rates.”

PGDIS’s response counters, “the ASRM opinions have taken into consideration neither contemporary literature nor facts that could have been provided by embryologists, geneticists and laboratories responsible for over 90 percent of these tests worldwide.” The group also states, “A beneficial effect requires experienced embryologists and geneticists who can obtain blastomeres and analyze single cells in optimal fashion. Considerable expertise is required.” This argument mirrors that in a paper a group of PGD providers published earlier in October, which made the case that poor technique accounted for the discouraging results of two recent randomized, controlled trials of PGS.

“This controversy underlines how little data we have on the efficacy of a widely-used and costly procedure,” says Susannah Baruch, the Center’s director of reproductive genetics. “We hope that in the near future we’ll have a registry of PGS and PGD procedures to help us answer such questions as whether PGS is useful, and if so, for whom.” – Shawna Williams

Preimplantation genetic testing: A Practice Committee opinion (subscription required)

Preimplantation Genetic Diagnosis International Society Refutes American Society of Reproductive Medicine Opinion

Article – Findings cast doubt on efficacy of PGD for aneuploidy

Issue brief – Oversight of preimplantation genetic diagnosis

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