Genetic screening and PGT

Advances in genetics make it possible to screen parents for common genetic conditions, lower the chance of passing inherited disease to children, and identify embryos with abnormal chromosomes before transfer.

What PGT is

Preimplantation genetic testing (PGT) can be added to IVF or ICSI to check embryos for genetic or chromosomal abnormalities before transfer, helping choose the embryos best suited for a healthy pregnancy. There are two main types:

• PGT-M tests embryos for a specific single-gene (monogenic) condition.
• PGT-A tests the number, and some aspects of the structure, of an embryo’s chromosomes, using next-generation sequencing (NGS).

Who may benefit from PGT

• People with a known genetic abnormality
• People affected by an inheritable disease
• Men with few or no sperm in the ejaculate
• Couples with recurrent pregnancy loss
• Patients with repeated implantation failure
• Women of advanced maternal age
• Patients with a good prognosis planning a single embryo transfer
• Families choosing sex selection

Genetic screening for parents

Carrier screening is a simple blood test that estimates the chance of passing a condition to your children. It’s available for a large group of disorders, including cystic fibrosis, sickle cell disease, spinal muscular atrophy (SMA), BRCA1 and BRCA2 (breast cancer genes), thalassemias, fragile X, the Ashkenazi Jewish panel and many others. Our goal is to detect common recessive conditions and, if one is found, minimize the chance of it reaching your baby.

When a man or woman may carry a genetic problem that standard screening doesn’t cover, such as Huntington disease or Marfan syndrome, we test specifically for that condition and arrange genetic counseling to assess the risk to future children.

Men with few or no ejaculated sperm have a higher risk of certain genetic findings, including chromosomal abnormalities such as Klinefelter syndrome, small missing segments (deletions) of the Y chromosome, and congenital absence of the vas deferens, the ducts that carry sperm from the testes.

How PGT is used

Single-gene conditions

If parents carry or are affected by an inheritable disease, or a previous child is affected, eggs or embryos can be tested, and unaffected embryos are transferred to avoid a pregnancy affected by the condition. This is PGT-M.

Sex-linked conditions and family balancing

Testing for the X and Y chromosomes can help avoid some sex-linked genetic diseases, or can be used for family balancing. Learn more about sex selection.

Recurrent pregnancy loss

When a parent carries a structural chromosome change that causes repeated miscarriage, such as a translocation (where part of one chromosome is attached to another), a few cells from each embryo can be tested for chromosome number and some structural abnormalities before transfer.

Chromosome testing and IVF outcomes

Not all human embryos are chromosomally normal. Each human cell has 46 chromosomes, and a significant proportion of embryos, whether conceived naturally or through IVF, have a chromosomal abnormality, most often an abnormal number of chromosomes. PGT-A can test all of an embryo’s chromosomes so that normal embryos can be selected for transfer.

Using PGT-A to improve IVF success for parents who don’t carry a chromosomal abnormality is still being studied.

Biopsy and testing

Depending on your situation and the genetic question being asked, material for testing can be collected at different stages:

• From the egg (polar body biopsy)
• From a day 3 embryo
• From the outer layer of a blastocyst (trophectoderm biopsy)

The type of test also depends on the goal:

• Testing for a specific single-gene condition, when the exact change is known from testing the parents or a previous child.
• Testing all of the embryo’s chromosomes, which looks at their number and structure but not at specific genes.

Genetic testing of embryos can greatly reduce the chance of passing a known condition to your children. Our genetic counselor is part of our team and can help you understand your options.

This article is general information, not medical advice. Every situation is different, so talk with your doctor about yours.