Antenatal Visits and Investigations MCQ — NEET PG Practice Question | NEETPGAI
Antenatal Visits and Investigations
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baby OBG
A 28-year-old primigravida at 16 weeks of gestation attends her first antenatal visit. She is asymptomatic with a normal obstetric examination. Her booking blood tests show: Hb 11.2 g/dL, blood group O positive, negative infectious serology (HIV, HBsAg, VDRL, rubella IgM). She has no significant past medical history. What is the most appropriate next investigation at this visit?
A. Detailed morphology scan
B. Quadruple marker screening (AFP, hCG, uE3, inhibin A)
C. Cell-free fetal DNA testing (NIPT)
D. Transvaginal ultrasound for nuchal translucency
Explanation
Investigation Timing and Appropriateness in Early Pregnancy
Gestational Age Context
At 16 weeks of gestation, the patient is in the second trimester. This is the optimal window for second-trimester biochemical screening.
Quadruple Marker Screening
Key Point
Quadruple marker screening (also called quad screen or quad test) is performed between 15 and 22 weeks of gestation, with optimal timing at 16–18 weeks.
High-YieldNEET PG
The quad screen measures four maternal serum markers:
Alpha-fetoprotein (AFP) — decreased in Down syndrome
Human chorionic gonadotropin (hCG) — elevated in Down syndrome
Unconjugated estriol (uE3) — decreased in Down syndrome
Inhibin A — elevated in Down syndrome
This combination detects approximately 80–85% of Down syndrome cases and 70% of Edwards syndrome (Trisomy 18) cases with a false-positive rate of ~5%.
Why Quad Screen at 16 Weeks?
Clinical Pearl
The quad screen is the standard first-tier screening test for chromosomal abnormalities in the second trimester in India and most resource-limited settings. It is cost-effective, non-invasive, and has good detection rates. At 16 weeks, the patient is at the ideal gestational age window.
Comparison with Other Options
Table
Investigation
Timing
Purpose
Indication
Nuchal translucency (NT)
11–14 weeks
First-trimester screening
First trimester; too late at 16 weeks
Quad screen
15–22 weeks (optimal 16–18)
Second-trimester screening
Standard at 16 weeks
NIPT (cfDNA)
10+ weeks
Non-invasive prenatal testing
High-risk pregnancies; not standard first-line in resource-limited settings
Detailed morphology scan
18–22 weeks
Anatomical assessment
Later in second trimester; done after biochemical screening
Mnemonic
QUAD = Quick Usefulness At Days 105–154 (15–22 weeks).
Rationale for Quad Screen Here
1.
Timing: 16 weeks is within the optimal window.
2.
Cost-effectiveness: Quad screen is affordable and widely available in India.
3.
Detection rate: 80–85% for Down syndrome.
4.
Non-invasive: No risk of miscarriage, unlike invasive testing.
5.
Standard of care: Recommended by RCOG, ACOG, and Indian guidelines for antenatal screening.
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