Estimation of maternal serum alpha-fetoprotein helps in diagnosis of all except :
**Core Concept**
Estimation of maternal serum alpha-fetoprotein (MSAFP) is a screening test used to detect potential fetal anomalies, particularly neural tube defects, and other conditions such as placental abnormalities.
**Why the Correct Answer is Right**
MSAFP is a protein produced by the yolk sac during early pregnancy. Elevated levels of MSAFP are associated with an increased risk of neural tube defects (e.g., spina bifida, anencephaly), whereas low levels may indicate other fetal anomalies or chromosomal abnormalities. The MSAFP level is also used to screen for placental abnormalities, such as placenta previa and placental abruption.
**Why Each Wrong Option is Incorrect**
**Option A:** **Trisomy 13** - Elevated MSAFP levels can be seen in trisomy 13, a chromosomal abnormality characterized by severe developmental delays and birth defects.
**Option C:** **Trisomy 18** - Elevated MSAFP levels are also associated with trisomy 18, a chromosomal abnormality characterized by severe developmental delays and birth defects.
**Clinical Pearl / High-Yield Fact**
Elevated MSAFP levels can be due to various causes, including multiple gestations, fetal demise, and certain fetal anomalies. A thorough ultrasound examination is essential to confirm the diagnosis and rule out other potential causes.
**Correct Answer: D. Trisomy 21**