FIRST TRIMESTER FETAL NUCHAL TRANSLUCENCY - PROBLEMS WITH SCREENING THE GENERAL-POPULATION .1.

Objective To evaluate the feasibility of measuring first trimester nuc hal translucency in an unselected population, to assess the relationsh ip with gestation and maternal age and to measure reproducibility. Des ign A prospective observational study. Setting University College Hosp ital, London. Subjects One thousand and four women attending for a rou tine first trimester dating scan between eight and thirteen weeks of g estation. Measurements of nuchal translucency were attempted in 1368 ( 80.3%) and successful in 1127 (82% of attempts). Results Nuchal transl ucency is most easily measured at 11 weeks of gestation. If a cut-off of greater than or equal to 3 mm is used, 6% of unselected fetuses bet ween eight and thirteen weeks of gestation are classified as abnormal. Nuchal translucency increases with gestational but not maternal age. Reproducibility is poor: by repeating measurements with a different op erator, the same operator using a different still image, or the same o perator using the same still image, 18.8%, 17.5% or 12.4% of nuchal tr anslucency measurements, respectively, change their classification as normal or abnormal. Conclusions If nuchal translucency greater than or equal to 3 mm were used as an indication for karyotyping, 6% of the n ormal pregnant population would be screen positive. However, the perce ntage will vary greatly depending on the gestational age profile of th e screened population. The poor reproducibility of nuchal translucency measurement could diminish its usefulness as a screening test for Dow n's syndrome.