Senior Consultant, Fetal Medicine, Artemis Hospitals, Gurgaon, India
Part 2 of 7 in Diagnostic Utility of First Trimester Ultrasound
Screening for Down Syndrome: How Detection Rates Evolved From 30% to 96%
June 21, 2026
Trisomy 21 remains the most common aneuploidy in ongoing pregnancies specifically because affected individuals have a long lifespan: unlike many chromosomal abnormalities, it doesn't typically end a pregnancy on its own, which places lasting stress on families and health systems. Maternal age alone catches only about 30% of cases, and 70 to 80% of Down syndrome babies are actually born to mothers under 35, which is why universal guidelines recommend screening every pregnant woman, regardless of age.
Detection rates climb as more markers are layered in: ultrasound examination alone reaches 60-70%; age plus nuchal translucency reaches 75-80%; adding the double marker biochemical test (PAPP-A and beta-hCG) reaches 85-95%; and the full FMF protocol (adding nasal bone, tricuspid flow and ductus venosus flow) reaches 93-96%, with a false positive rate of just 2.5%. Screening is done when the crown-rump length is between 60 and 84mm, around 12 weeks.
This guide is based on a live Jivo Masterclass — Dr. Aanchal Sablok taught doctors across Africa on June 21, 2026.
FROM THE LIVE Q&A
How does the stage of CKD (chronic kidney disease) affect the risk of preeclampsia?
Dr. Aanchal Sablok
If the mother already has chronic kidney disease, she is already at risk of chronic hypertension. When placental implantation occurs on top of this background, the relevant terminology is preeclampsia superimposed on chronic hypertension. This represents an even higher risk of developing preeclampsia, particularly in the presence of chronic renal disease, chronic hypertension, or other conditions such as autoimmune disease. The risk of fetal growth restriction (small for gestational age) is also correspondingly higher in this group.
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Frequently Asked Questions
Why is Down syndrome the most common chromosomal abnormality found in ongoing pregnancies?▼
Trisomy 21 remains the most common aneuploidy in ongoing pregnancies because affected individuals have a long lifespan. Unlike many chromosomal abnormalities, it does not typically end a pregnancy on its own, which places lasting stress on families and health systems.
Is maternal age a reliable way to screen for Down syndrome?▼
No. Maternal age alone catches only about 30% of cases, and 70 to 80% of Down syndrome babies are actually born to mothers under 35. This is why universal guidelines recommend screening every pregnant woman regardless of age.
How much does combining ultrasound with biochemical markers improve detection?▼
Detection climbs as more markers are layered in. Ultrasound alone reaches 60 to 70%, age plus nuchal translucency reaches 75 to 80%, and adding the double marker biochemical test (PAPP-A and beta-hCG) reaches 85 to 95%.
What detection rate does the full FMF protocol achieve, and what is its false positive rate?▼
The full FMF protocol, adding nasal bone assessment, tricuspid flow and ductus venosus flow to the earlier markers, reaches 93 to 96% detection with a false positive rate of just 2.5%.
When should Down syndrome screening be performed?▼
Screening is done when the crown-rump length is between 60 and 84mm, which corresponds to around 12 weeks of gestation.
In This Series: Diagnostic Utility of First Trimester Ultrasound
- 1.Diagnostic Utility of First Trimester Ultrasound
- 2.Screening for Down Syndrome: How Detection Rates Evolved From 30% to 96%
- 3.Nuchal Translucency: Why a High Reading Doesn't Mean What Patients Fear
- 4.Structural Abnormalities the First-Trimester Scan Can Already Catch
- 5.Preeclampsia Screening: Uterine Artery Doppler, PLGF, and the New Role of the Ophthalmic Artery
- 6.Predicting Preterm Labour: Why Cervical Length Should Be Measured at 12 Weeks
- 7.The Inverted Pyramid of Care: Rethinking When Pregnant Women Should Be Seen