What should I do if the Down syndrome screening indicates a high risk for trisomy 21?

Down syndrome screening—commonly referred to as “Down screening”—is a prenatal screening test for Down syndrome. It involves analyzing the mother’s blood to measure serum levels of alpha-fetoprotein (AFP), human chorionic gonadotropin (hCG), and unconjugated estriol (uE3), combined with maternal factors such as age, weight, and gestational age, to estimate the risk of the fetus having Down syndrome (trisomy 21) or neural tube defects. So, what should be done if Down screening indicates a high risk for trisomy 21? The following section addresses this question.

What to Do If Down Screening Indicates High Risk for Trisomy 21

Generally speaking, Down screening yields a probabilistic result—not a definitive diagnosis. It estimates the likelihood of the fetus having Down syndrome based on maternal serum markers, gestational age, maternal weight, and other parameters. A “high-risk” result does not equate to a confirmed diagnosis. Specifically, a calculated risk greater than 1 in 270 is considered high risk, indicating an elevated probability that the fetus has Down syndrome. When Down screening returns a high-risk result, further diagnostic or confirmatory tests are recommended—namely, non-invasive prenatal testing (NIPT) or amniocentesis. NIPT involves drawing a peripheral blood sample from the mother to isolate cell-free fetal DNA circulating in her bloodstream, then analyzing chromosomes 21, 18, and 13 for numerical abnormalities. Amniocentesis, by contrast, involves extracting amniotic fluid to culture fetal cells and perform chromosomal karyotyping; it provides a definitive diagnostic result. NIPT, while highly accurate, remains a screening tool—not a diagnostic test.

Knowledge Expansion: What Conditions Does Down Screening Primarily Detect?

1. Chromosomal Abnormalities

Down screening primarily assesses whether the fetus has chromosomal abnormalities—most commonly trisomy 18 (Edwards syndrome) and trisomy 21 (Down syndrome). Early identification helps significantly reduce the risk of severe congenital anomalies resulting from chromosomal disorders.

2. Open Neural Tube Defects (ONTDs)

Open neural tube defects include conditions such as meningocele. Down screening reports typically classify results as low risk, high risk, or borderline (intermediate) risk. A high-risk result raises significant concern and warrants further investigation—typically via amniocentesis or NIPT—to definitively determine whether the fetus has any chromosomal or structural abnormalities.

The above outlines the appropriate steps to take when Down screening indicates a high risk for trisomy 21. We hope this information proves helpful.