[Sonographic features of chromosomal defects at 11(+0) to 13(+6) weeks of gestation].

Each chromosomal defect has its own syndromal pattern of detectable abnormalities. The authors describe the sonographic features of trisomy 21 and other major chromosomal defects in the first trimesters of pregnancy. At 11(+0) - 13(+6) weeks, all major chromosomal defects are associated with increased NT thickness. In trisomies 21, 18 and 13 the pattern of increase in NT is similar and the average NT in these defects is about 2.5 mm above the normal median for crown-rump length. In Turner syndrome, the median NT is about 8 mm above the normal median. In addition to increased NT there are sonographic features that are often seen in some affected fetuses at 11(+0) - 13(+6) weeks. In trisomy 21 fetuses have absent nasal bone, short maxilla and abnormal Doppler waveforms in the ductus venosus. In trisomy 18, there is early onset fetal growth restriction, a tendency for bradycardia, exomphalos, absent nasal bone and single umbilical artery. In trisomy 13, there is tachycardia, early onset fetal growth restriction, megacystis, holoprosencephaly and exomphalos. In Turner syndrome, there is tachycardia and early onset fetal growth restriction. In triploidy, there is early onset asymmetrical fetal growth restriction, bradycardia, holoprosencephaly, exomphalos, posterior fossa cyst and molar changes in the placenta.