A physician-validated, board-style question from the Active Transport QBank. Try it, then check the reasoning for every option.
A 23-year-old pregnant woman (gravida 1, para 0) presents during her 16th week of pregnancy for a check-up. The course of her current pregnancy is unremarkable. She had normal results on the previous ultrasound examination. Her human chorionic gonadotropin (hCG) level measured at week 12 of pregnancy was 0.9 multiples of the normal median (MoM). She is human immunodeficiency virus (HIV), hepatitis B virus (HBV), and hepatitis C virus (HCV)-negative. She undergoes a quadruple test which shows the following results:
Serum alpha-fetoprotein Low
Unconjugated estriol Low
Beta-hCG High
Inhibin A High
The risk of which condition indicates these results?
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A
Trisomy 21Correct. The 'high beta-hCG, high inhibin A, low AFP, low estriol' pattern is the textbook quadruple-screen signature of trisomy 21.
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B
Neural tube defectIncorrect. Neural tube defects show elevated maternal serum AFP, not low AFP — and would not affect inhibin A or hCG in this pattern.
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C
Congenital toxoplasmosisIncorrect. Congenital toxoplasmosis is not screened by the quadruple test; diagnosis is by maternal IgM/IgG serology or amniotic fluid PCR.
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D
Trophoblastic diseaseIncorrect. Trophoblastic disease (molar pregnancy) features markedly elevated beta-hCG without the AFP/estriol pattern described and typically presents earlier with hyperemesis, bleeding, and uterine size > dates.
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E
Trisomy 18Incorrect. Trisomy 18 (Edwards syndrome) shows low AFP, low beta-hCG, low estriol, and normal/low inhibin A on the quadruple screen — not the high beta-hCG and high inhibin A described here.
↑ Tap an answer to reveal the reasoning
Answer: A. The quadruple screen pattern of low maternal serum AFP, low unconjugated estriol, high beta-hCG, and high inhibin A is the classic profile of trisomy 21 (Down syndrome). Each marker reflects altered placental and fetal endocrine function: low AFP and estriol from impaired fetal/placental synthesis, and elevated beta-hCG and inhibin A from a hyperactive trophoblast.
This screening is performed at 15–20 weeks gestation. Note her first-trimester hCG (week 12) was low at 0.9 MoM — in the first trimester, trisomy 21 is screened with PAPP-A (low), free beta-hCG (high), and nuchal translucency (increased). Different patterns flag different aneuploidies: trisomy 18 shows low AFP, estriol, and hCG, with normal inhibin A; neural tube defects show high AFP without changes in the other markers.
Clinical pearl: positive screening prompts diagnostic confirmation with cell-free fetal DNA or invasive testing (chorionic villus sampling or amniocentesis) for definitive karyotype.
**Why each option:**
**A.** The 'high beta-hCG, high inhibin A, low AFP, low estriol' pattern is the textbook quadruple-screen signature of trisomy 21.
**B.** Neural tube defects show elevated maternal serum AFP, not low AFP — and would not affect inhibin A or hCG in this pattern.
**C.** Congenital toxoplasmosis is not screened by the quadruple test; diagnosis is by maternal IgM/IgG serology or amniotic fluid PCR.
**D.** Trophoblastic disease (molar pregnancy) features markedly elevated beta-hCG without the AFP/estriol pattern described and typically presents earlier with hyperemesis, bleeding, and uterine size > dates.