Optimal crown-rump length for measuring the nuchal translucency

Area of Science:

• Maternal-fetal medicine
• Prenatal screening
• Diagnostic ultrasound

Background:

• Nuchal translucency (NT) measurement is a key component of first-trimester combined screening for chromosomal abnormalities.
• Optimizing NT measurement success is crucial for accurate risk assessment in early pregnancy.

Purpose of the Study:

• To identify the optimal crown-rump length (CRL) range for maximizing the success rate of nuchal translucency (NT) measurements.
• To evaluate the impact of CRL on NT measurement success and screening outcomes.

Main Methods:

• Retrospective analysis of 837 NT measurements from a combined screening program over 18 months.
• Comparison of NT measurement success, screen-positive rates, and transvaginal sonography (TVUS) use across three CRL groups: 45-54 mm (11-12 weeks), 55-66 mm (12 weeks), and 67-84 mm (13 weeks).

Main Results:

• NT measurement success rates were significantly higher at 11 and 12 weeks (81.8% and 84.4%) compared to 13 weeks (66.9%) (p < 0.001).
• No significant differences were observed in screen-positive rates, TVUS use, or reasons for failed NT measurements across the studied CRL groups.

Conclusions:

• Nuchal translucency (NT) measurements achieve the highest success rates when the fetal crown-rump length (CRL) is between 45-66 mm.
• This optimal CRL range corresponds to a sonographically determined gestational age of 11 weeks and 0 days to 12 weeks and 6 days.