FAQ Genetics

• Studies of fertility treatments have shown that a significant proportion of the embryos produced during the course of in vitro fertilization (IVF) treatment are incapable of forming a healthy pregnancy. One of the main reasons why some embryos cannot produce a baby is the presence of a chromosome abnormality (see Chromosomes and Aneuploidy for more information).
• In most cases, embryos that have an abnormal number of chromosomes in their cells cannot implant in the womb or miscarry during the first trimester of pregnancy. Unfortunately, chromosomally abnormal embryos are usually indistinguishable from their normal counterparts using the microscopic (morphological) assessments routinely carried out in IVF laboratories. This is why embryologists cannot always identify them and may inadvertently select them for transfer to the womb.
• By testing embryos for chromosome abnormalities, the likelihood of achieving a healthy pregnancy is increased and the risk of miscarriage and aneuploidy conception is decreased.

Most early pregnancy losses can be attributed to aneuploidy. Because only chromosomally normal embryos are transferred into the uterus, the risk of first and second trimester loss is markedly reduced. Primary candidates for PGD can include the following:

• Women of advanced maternal age.
• Couples with chromosome translocations, which can cause implantation failure, recurrent pregnancy loss, or mental or physical problems in offspring .
• Couples with history of recurrent pregnancy loss.
• Couples with repeated IVF failure.
• Male partner with severe male factor infertility.

Preimplantation genetic diagnosis (PGD) is recommended when couples are at risk of transmitting a known genetic abnormality to their children. Only healthy and normal embryos are transferred into the mother’s uterus, thus diminishing the risk of inheriting a genetic abnormality and late pregnancy termination (after positive prenatal diagnosis).Primary candidates for PGD can include the following:

• Couples with a family history of X-linked disorders (Couples with a family history of X-linked disease have a 25% risk of having an affected embryo [half of male embryos].) for e.g. hemophilia, fragile X syndrome, most neuromuscular dystrophies (currently, >900 neuromuscular dystrophies are known), Rett syndrome, incontinentia pigmenti, pseudohyperparathyroidism, Glucose 6 phosphate dehydrogenase deficiency and vitamin D–resistant rickets etc.
• Carriers of autosomal recessive diseases (For carriers of autosomal recessive diseases, the risk an embryo may be affected is 25%.) for e.g. cystic fibrosis, Tay-Sachs disease, sickle cell anemia, Thalassemia and Spinal muscular atrophy etc.
• Carriers of autosomal dominant diseases (For carriers of autosomal dominant disease, the risk an embryo may be affected is 50%.) for e.g. Huntington’s disease, neurofibromatosis type 1, neurofibromatosis type 2 and Marfan syndrome etc.