Maternal Alpha-fetoprotein concentration in serum is elevated in all except :
**Core Concept**
Maternal Alpha-fetoprotein (AFP) is a protein produced by the fetus during pregnancy, and its concentration in maternal serum is used as a screening test for fetal abnormalities and gestational age. Elevated AFP levels can indicate potential issues such as neural tube defects, chromosomal abnormalities, or multiple gestations.
**Why the Correct Answer is Right**
In a normal pregnancy, AFP levels gradually increase until around 32 weeks of gestation, after which they decline. Elevated AFP levels can be seen in conditions where fetal development is abnormal, such as in neural tube defects like spina bifida or anencephaly. Additionally, chromosomal abnormalities such as Down syndrome or trisomy 18 can also lead to increased AFP levels. Multiple gestations, where more than one fetus is present, can also cause elevated AFP levels due to the increased production of AFP by multiple fetuses.
**Why Each Wrong Option is Incorrect**
**Option A:** This option is incorrect because AFP levels can be elevated in multiple gestations, where more than one fetus is present.
**Option B:** This option is incorrect because AFP levels can be elevated in chromosomal abnormalities such as Down syndrome or trisomy 18.
**Option C:** This option is incorrect because AFP levels can be elevated in neural tube defects like spina bifida or anencephaly.
**Clinical Pearl / High-Yield Fact**
It's essential to note that while elevated AFP levels can indicate potential issues, they are not diagnostic on their own and require further testing, such as ultrasound or amniocentesis, to confirm the presence of a fetal abnormality.
**Correct Answer: D.**