A 28-year-old primigravida at 16 weeks of gestation presents for her second antenatal visit. Her first-trimester screening (combined test) shows a risk of 1 in 250 for Down syndrome. She is anxious and requests further testing. Her detailed anomaly scan is normal. What is the most appropriate next step in management?
A. Perform amniocentesis immediately
B. Refer for termination of pregnancy counselling
C. Offer cell-free fetal DNA testing (non-invasive prenatal testing)
D. Repeat the combined screening test
Explanation
Clinical Context
The patient has an intermediate-risk result (1 in 250) from first-trimester combined screening. At 16 weeks, she is past the optimal window for first-trimester screening but well within the window for second-trimester testing options.
Management Algorithm for Abnormal Screening
Key Point
Cell-free fetal DNA testing (cfDNA / NIPT) is now the recommended second-line test for intermediate-risk pregnancies, offering superior detection rates (>99% for trisomy 21) with minimal risk.
High-YieldNEET PG
NIPT can be performed from 10 weeks onwards and is non-invasive. It has a false-positive rate of <0.1% for trisomy 21 when performed in a low-risk population.
Clinical Pearl
A normal detailed anomaly scan does NOT exclude chromosomal abnormalities; structural markers may appear later or be subtle. The risk remains elevated based on biochemical screening.
Why NIPT is Next Best Step
Table
Aspect
NIPT (cfDNA)
Amniocentesis
Repeat Combined Test
Timing at 16 weeks
Appropriate
Invasive, 1% miscarriage risk
Too late for optimal accuracy
Detection rate (T21)
>99%
>99%
Already done; repeat unhelpful
Miscarriage risk
None
~1 in 200–400
N/A
Recommended sequence
First-line for intermediate risk
Only if NIPT abnormal or declined
Not recommended
Mnemonic
NIPT FIRST — Non-invasive, Intermediate-risk, Preferred, Then invasive if needed; First-line for counselling; Intermediate-risk; Risk reduction; Second-trimester option; Timing flexible.
Rationale
1.
NIPT offers the best balance of detection and safety for intermediate-risk pregnancies.
2.
It allows the patient to make an informed decision without exposing the fetus to procedural risk.
3.
If NIPT is abnormal, amniocentesis can then be offered for diagnostic confirmation.
4.
Normal detailed anatomy scan does not change the biochemical risk and does not negate the need for further testing.
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