First trimester fetal nuchal translucency: problems with screening the general population. 1

Area of Science:

• Prenatal diagnostics
• Fetal medicine
• Maternal-fetal medicine

Background:

• First-trimester nuchal translucency (NT) measurement is a key component of Down syndrome screening.
• Assessing the feasibility and reliability of NT measurement in an unselected population is crucial for its clinical application.

Purpose of the Study:

• To evaluate the feasibility of measuring first-trimester nuchal translucency in an unselected population.
• To assess the relationship between NT, gestational age, and maternal age.
• To determine the reproducibility of NT measurements.

Main Methods:

• Prospective observational study conducted at University College Hospital, London.
• NT measurements were attempted in 1368 women undergoing routine first-trimester dating scans (8-13 weeks gestation).
• Reproducibility was assessed by multiple operators and image selections.

Main Results:

• NT measurement was successful in 82% of attempts, with optimal measurement at 11 weeks gestation.
• A threshold of ≥3 mm classified 6% of fetuses as abnormal; NT increased with gestation but not maternal age.
• Poor reproducibility was observed, with 12.4-18.8% of measurements changing normal/abnormal classification based on operator and image selection.

Conclusions:

• Using NT ≥3 mm for karyotyping would result in a 6% screen-positive rate in the general pregnant population.
• The poor reproducibility of NT measurements could significantly impact its utility as a screening test for Down syndrome.
• Variability in screen-positive rates depends on the gestational age distribution of the screened population.