Fetal thickened nuchal soft tissues may first appear in the second trimester in Down syndrome

Purpose. To describe a series of cases of late-onset fetal nuchal translucency in Down syndrome. Method. In our practice area, most pregnant women usually undergo 3 different sonographic examinations: a fetal nuchal translucency examination in the 1st trimester and 2 detailed surveys of all fetal organs in the early 2nd trimester and in midpregnancy. Result. During the study period (2003-2008), we detected 11 fetuses with new appearance of severe thickened nuchal soft tissues (≥6 mm) at 14-16 weeks' gestation after a normal nuchal screening in the 1st trimester. All of these fetuses had trisomy 21. Associated structural anomalies were observed in 10/11 of the cases. In addition, there were 12 fetuses with new appearance of thickened nuchal soft tissues (< 4 mm); all these fetuses had a normal karyotype and were normal at delivery. Conclusion. Obstetricians should be aware that a nuchal abnormality may first appear only at 14-16 weeks' gestation. Fetal karyotyping is advocated in these cases because of the high probability of Down syndrome.