Maternal Serum Screening (Triple Screen) and Chromosomal Abnormalities
Overview of Triple Screen
Key Point
The triple screen (performed at 15–20 weeks) measures three maternal serum markers:
Marker Pattern in Trisomy 21
| Marker | Pattern in Down Syndrome | Mechanism |
|---|
| AFP | ↓ Decreased | Reduced fetal production |
| hCG | ↑ Increased | Elevated placental secretion |
| uE3 | ↓ Decreased | Reduced fetal adrenal synthesis |
| Inhibin A | ↑ Increased | (Quadruple screen adds this) |
Prevalence of Chromosomal Abnormalities
| Abnormality | Prevalence at Birth | Detection Rate by Triple Screen |
|---|
| Trisomy 21 | 1 in 700–1000 | 60–70% (75–85% with quad screen) |
| Trisomy 18 | 1 in 6000 | 60% |
| Trisomy 13 | 1 in 10,000 | 50% |
| Turner syndrome | 1 in 2000–2500 | <10% (not reliably detected) |
High-Yield Facts
High-YieldNEET PG
Trisomy 21 is the most common viable chromosomal abnormality at birth and the most frequently detected by maternal serum screening. It accounts for ~50% of all chromosomal abnormalities in the antenatal period.
Key Point
The triple screen has a detection rate of 60–70% for Down syndrome at a 5% false-positive rate. The quadruple screen (adding inhibin A) improves detection to 80–85%.
Clinical Pearl
Clinical Pearl
In the Indian population, advanced maternal age (>35 years) and consanguinity increase the risk of trisomy 21. Screening should be offered to all pregnant women regardless of age, as ~80% of Down syndrome cases occur in women <35 years.
Management Algorithm
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Mnemonic: Down 21 — Decreased AFP, Decreased uE3, Up hCG, Need further testing.
