PGD and PGS

Preimplantation Genetic Screening and Diagnosis

Genetic testing can help increase the chances of a healthy pregnancy by screening the potential parents and/or embryos for potential genetic problems. There are two types of genetics tests available: preimplantation genetic screening (PGS) and preimplantation genetic diagnosis (PGD).

PGS tests broadly for multiple genetic problems that could be present. PGD, on the other hand, is a diagnostic test that searches for a specific genetic disease known to be present in one or both partners’ families. Thousands of diseases can be detected through either PGS or PGD testing.

The most frequently diagnosed diseases and disorders found through genetic testing are:

  • Charcot-Marie tooth disease
  • Cystic fibrosis
  • Duchenne muscular dystrophy
  • Fragile X syndrome
  • Hemophilia A
  • Huntington’s disease
  • Myotonic dystrophy
  • Sickle cell anemia
  • Spinal muscular atrophy
  • Tay-Sachs Disease
  • Thalassemia

Who should consider preimplantation genetic diagnosis

  • Couples who already have a child with a genetic problem and are at high risk of having another with the same problem.
  • Couples who know that one or both members have a genetic problem with known transmission to offspring.

Gender selection for genetic disorders

Preimplantation genetic testing (PGD and PGS) can also detect the sex of an embryo. This is beneficial to the diagnostic process because more than 200 disorders can be prevented simply through gender selection. For instance, gene disorders like Duchenne muscular dystrophy or hemophilia only occur in males. Therefore, to reduce the risk of having an affected child, the PGD/PGS of the biopsied embryonic cell can determine gender, and only female embryos can be transferred into the mother’s uterus, thereby eliminating the risk of gender-associated genetic disorders.

In 1994, the Ethics Committee of the American Society of Reproductive Medicine concluded that preimplantation sex selection is only appropriate to avoid the birth of children with genetic disorders. The committee deemed gender selection for nonmedical reasons unacceptable.

Who should consider preimplantation genetic screening

PGS is more controversial. Most large studies that have evaluated PGS as a way to reduce miscarriage have failed to show a benefit and in fact have shown lower pregnancy rates in the screened population. In the future, improvements in technology may show a benefit, but currently PGS is considered experimental and should be used only after rigorous counseling.