FIRST-TRIMESTER SONOGRAPHIC DETECTION OF CHROMOSOMAL-ABNORMALITIES INAN UNSELECTED POPULATION

Objective To investigate the role of first trimester sonography in det ecting chromosomal abnormalities in an unselected obstetric population . Methods 2281 women (mean maternal age 30 years [range 16-47]; mean g estational age 12(+3) weeks [range 11-14]) underwent transabdominal sc anning to assess fetal structure and, if anatomical survey was conside red to be incomplete (31% of cases), transvaginal sonography was also performed. Measurement of nuchal translucency was included and karyoty ping performed as considered appropriate. Results There were 16 chromo somal abnormalities; 13 (81%) were diagnosed at 11-14 weeks either bec ause of a nuchal translucency greater than or equal to the 99th centil e for gestational age (7/16; 44% [95% CI 25-63]) or due to the presenc e of structural abnormalities (6/16; 38% [95% CI 14.2-61.8]), Seventy- five percent of cases of trisomy 21 were also diagnosed either because of having a nuchal translucency greater than or equal to the 99th cen tile (5/8; 63%) or due to the presence of a structural abnormality (1/ 8; 13%). Conclusions A significant proportion of fetal chromosomal abn ormalities can be detected by first trimester sonographic screening to assess fetal structural appearance. The sensitivity of detection can be improved by combining measurement of nuchal translucency with detai led examination of fetal anatomy.