How do you know if you have Down syndrome during pregnancy?

During pregnancy, Down syndrome can be detected through a combination of screening and diagnostic tests that analyze genetic markers and physical indicators.

Understanding Down Syndrome Detection in Pregnancy

The process of detecting Down syndrome during pregnancy typically involves two main types of tests: screening tests and diagnostic tests. Screening tests are non-invasive and estimate the likelihood of Down syndrome, while diagnostic tests are invasive but provide a definitive answer by analyzing the baby's chromosomes directly.

Screening Tests: Assessing Your Baby's Risk

Screening tests do not diagnose Down syndrome but can indicate an increased risk, prompting further discussion about diagnostic options. They are safe for both the mother and the baby.

• First Trimester Combined Screen: This screen is typically performed between weeks 11 and 14 of pregnancy and includes two parts:
  • Blood Test: Measures levels of specific substances in the mother's blood, such as pregnancy-associated plasma protein-A (PAPP-A) and human chorionic gonadotropin (hCG).
  • Nuchal Translucency (NT) Ultrasound: This specialized ultrasound measures the clear space (fluid) at the back of the baby's neck. An increased measurement can sometimes indicate Down syndrome. When performed together during the first trimester, this combined method offers effective detection rates.
• Second Trimester Quad Screen: This blood test is usually performed between weeks 15 and 20 of pregnancy and measures four substances in the mother's blood: alpha-fetoprotein (AFP), unconjugated estriol (uE3), hCG, and inhibin A.
• Non-Invasive Prenatal Testing (NIPT) / Cell-Free DNA Testing: This advanced blood test, typically available after 10 weeks of pregnancy, analyzes small fragments of the baby's DNA circulating in the mother's bloodstream. It is highly accurate for detecting common chromosomal conditions, including Down syndrome (Trisomy 21).

Diagnostic Tests: Confirming a Diagnosis

Diagnostic tests are invasive procedures that carry a small risk of complications, such as miscarriage, but they provide a definitive diagnosis of Down syndrome by directly examining the baby's chromosomes.

• Chorionic Villus Sampling (CVS):
  • Timing: Typically performed between weeks 10 and 13 of pregnancy.
  • Procedure: A small sample of tissue is taken from the placenta for genetic analysis. This can be done either through the abdomen or the cervix.
• Amniocentesis:
  • Timing: Usually performed between weeks 15 and 20 of pregnancy.
  • Procedure: A small amount of amniotic fluid, which contains fetal cells, is collected from around the baby using a thin needle inserted through the abdomen. These cells are then analyzed for chromosomal abnormalities.

What Happens After Screening?

If a screening test indicates an increased risk for Down syndrome, your healthcare provider will discuss these diagnostic testing options. These tests can confirm or rule out the condition, providing you with definitive information about your baby's health.