A woman asks when the combined first-trimester screening test for Down syndrome can be performed in the NHS Fetal Anomaly Screening Programme. What is the correct window?
Answer and explanation
Correct answer: C. Between 11 weeks 2 days and 14 weeks 1 day
- Step 1: The combined test uses nuchal translucency on ultrasound plus maternal blood markers.
- Step 2: Crown-rump length must be within the range for the scan, which corresponds to 11 weeks 2 days to 14 weeks 1 day.
Answer
Between 11 weeks 2 days and 14 weeks 1 day.
Why not the others: Between 16 and 20 weeks: The nuchal scan window closes at 14 weeks 1 day, so it cannot be done at 16 to 20 weeks. Between 28 and 32 weeks: Growth and Doppler scans in the third trimester are not screening for Down syndrome. Between 6 and 8 weeks: Nuchal translucency cannot be measured at 6 to 8 weeks and the blood tests need the scan.
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