Ear length in trisomy 21 fetuses at 11-14 weeks of gestation.

OBJECTIVE To determine the value of measuring fetal ear length at 11-14 weeks of gestation in screening for chromosomal defects. METHODS The fetal ear length was measured in 450 fetuses immediately before chorionic villus sampling for karyotyping at 11-14 weeks of gestation. RESULTS The median gestational age was 12 (range, 11-14) weeks. The fetal ear was successfully examined in all cases. The fetal karyotype was normal in 409 cases and abnormal in 41, including 32 cases of trisomy 21. In the chromosomally normal group the fetal ear length increased significantly with crown-rump length from a mean of 3.7 mm at 45 mm to 6.9 mm at 84 mm. In the trisomy 21 fetuses the median ear length was significantly below the normal mean for crown-rump length by 0.45 mm (P = 0.013) but it was below the 5(th) centile of the normal range in only two (6.3%) of the cases. There was no significant association between the delta score of ear length and delta nuchal translucency in either the chromosomally normal (r = - 0.015, P = 0.753) or the trisomy 21 fetuses (r = - 0.014, P = 0.94). CONCLUSIONS At 11-14 weeks of gestation the ear length in trisomy 21 fetuses is significantly reduced but the degree of deviation from normal is too small for this measurement to be useful in screening for trisomy 21.