What Types of Genetic Testing Are Available During Pregnancy?

Pregnancy brings with it an array of questions and emotions. One important consideration is the health of your developing baby. Prenatal testing and diagnosis offer valuable information about potential genetic disorders or birth defects your foetus may have. This blog will explain the different types of prenatal genetic testing available to you.

What is Prenatal Genetic Testing?

Prenatal genetic testing provides insights into the foetus’s genetic makeup, looking for abnormalities that might lead to congenital disorders. Unlike routine prenatal tests like blood type or glucose screening, these tests are optional and require thorough discussion with healthcare providers to decide which tests are appropriate.

Prenatal genetic testing can be divided into two categories: screening tests and diagnostic tests.

Prenatal Screening Tests

Screening tests help to estimate the risk of the foetus having genetic conditions but do not provide definitive diagnoses. If a screening test result is abnormal, it suggests a higher risk for a genetic disorder, prompting healthcare providers to recommend further diagnostic testing.

1.      Carrier Screening:

Carrier screening is a blood test offered to both parents. It identifies changes in genes that could increase the risk of the foetus inheriting serious medical conditions such as cystic fibrosis, sickle cell disease, and spinal muscular atrophy. If one parent is a carrier, the other parent should also undergo screening to determine the risk to the foetus.

2.      Screening for Chromosomal Abnormalities:

• Cell-free Foetal DNA Screening (NIPT): This non-invasive test, performed from the 10th week of gestation, examines small fragments of foetal DNA in the mother’s blood to detect common chromosomal abnormalities like Down syndrome.
• Serum Screening: These blood tests analyse protein levels to assess the risk for chromosomal abnormalities. Types include sequential screening, quad screening, and first-trimester serum screening. They are typically performed between the 11th and 22nd weeks of pregnancy.

3.      Screening for Physical Abnormalities:

• Nuchal Translucency: An ultrasound performed between 11 and 14 weeks of gestation measures the thickness of the foetus’s neck. Increased thickness may indicate a higher risk for chromosomal abnormalities and physical defects. Moreover, a doctor can recommend Edwards’ syndrome, Patau’s syndrome, and Down syndrome tests to determine chromosomal abnormalities.
• AFP Screening (Maternal Serum Screen): This blood test, conducted between 15 and 22 weeks of gestation, measures the alpha-fetoprotein (AFP) in the mother’s blood. High AFP levels may indicate physical abnormalities in the foetus’s abdomen, face, or spine.
• Quad Screen: This test, performed between 15 and 22 weeks of pregnancy, measures four substances in the mother’s blood to assess the risk of chromosomal abnormalities and neural tube defects.
• Foetal Anatomy Scan: An ultrasound performed at 18 to 20 weeks of gestation to evaluate the foetus’s physical structures, including the brain, heart, skeleton, and other organs.

Prenatal Diagnostic Tests

Diagnostic tests provide a definitive diagnosis of genetic conditions. These tests involve analysing cells from the amniotic fluid or placenta. Diagnostic testing is recommended following an abnormal screening test result or for those at high risk for genetic conditions.

Common Diagnostic Tests:

• Amniocentesis: Conducted between 16 and 20 weeks of pregnancy, this test involves inserting a needle into the uterus to collect a sample of amniotic fluid. The sample is then analysed for genetic disorders.
• Chorionic Villus Sampling (CVS): Performed between 11 and 13 weeks of pregnancy, CVS involves taking a small sample of cells from the placenta. Depending on safety, the sample is collected through the abdomen or vagina.

Who Should Get Genetic Testing?

The decision to undergo prenatal genetic testing is personal and should be made after consulting a healthcare provider. Genetic testing can provide valuable information about the health of the foetus. It is generally offered to all pregnant families, but specific reasons for opting for diagnostic testing include:

• Abnormal screening test results
• Family history of genetic disorders
• Age (pregnancy over 35)
• History of miscarriage or stillbirth

Prenatal testing and diagnosis help parents make informed decisions and prepare for potential health issues their baby may face.