对染色体数目异常的胎儿，主要是常染色体三体型，在怀孕第７０９１天，通过Ｂ超作顶臀长（座高）的测量，研究胎儿的早期发育情况。对９６例异常儿与４００例正常胎儿对比研究，发现１８三体型胎儿顶臀长明显减小，结合其它指标可作为临床诊断参考，而１３三体型和２１三体型减小不明显，临床意义不大。 Abnormal fetal chromosome number, mainly autosomal trisomy, 7091 days of pregnancy by B-top hip (seat height) measurements to study the early development of the fetus. Contrast study of 96 cases of abnormal fetus with 400 cases of normal fetus, we found that the top of the trisomy 18 had a significant decrease in the top-rump length, combined with other indicators can be used as a reference for clinical diagnosis, while trisomy 13 and trisomy 21 were not significantly reduced, the clinical significance Big.