A Guide to Prenatal Genetic Testing and Diagnosis

There are two main categories of tests: screening and diagnostic.

A. Screening Tests : These assess the likelihood that your baby has a condition but don’t provide a definitive diagnosis.

• First Trimester Screening (11–14 weeks):
  Combines a blood test and an ultrasound (nuchal translucency) to check for chromosomal abnormalities like Down syndrome.
  
• Non-Invasive Prenatal Testing (NIPT):
  A simple blood test that analyzes fetal DNA from the mother’s bloodstream. It screens for Down syndrome, trisomy 18, trisomy 13, and sex chromosome conditions as early as 10 weeks.
  
• Second Trimester Quad Screen (15–20 weeks):
  Measures four substances in the mother’s blood to assess the risk of certain birth defects, including neural tube defects.
  

Note: Screening tests do not diagnose a condition—they only indicate risk levels. If a screening result is abnormal, your doctor may recommend a diagnostic test.

B. Diagnostic Tests : These offer a clear diagnosis and are usually recommended when there is a high-risk screening result or a family history of genetic conditions.

• Chorionic Villus Sampling (CVS):
  Performed between 10–13 weeks, this test takes a small sample of placental tissue to analyze chromosomes and genes.
  
• Amniocentesis:
  Done between 15–20 weeks, it involves collecting a small amount of amniotic fluid to detect genetic and neural tube disorders.
  

These tests are highly accurate, but they are invasive and carry a small risk of miscarriage. Your healthcare provider will discuss the risks and benefits with you in detail.