Increased nuchal translucency in trisomy 13 fetuses at 10-14 weeks of gestation

In a multicenter screening study for trisomy 21 involving ultrasonographic measurement of fetal nuchal translucency thickness (NT) at 10-14 weeks of g estation, 100,311 singleton pregnancies with a live fetus were examined. Th ere were 46 cases of trisomy 13, and in 33 (72%) of these, the NT was above the 95th centile, The estimated risk for trisomy 21, based on maternal age -related risk for this chromosomal abnormality and fetal NT, was above 1 in 300 in 37 (80.1%):of the trisomy 13 fetuses. The fetal crown-rump length w as significantly reduced, but the fetal heart rate was increased, being abo ve the 95th centile in 64% of cases. Additionally, 24% of trisomy 13 fetuse s had holoprosencephaly and 10% had exomphalos. This study has demonstrated that at 10-14 weeks of gestation, about 80% of fetuses with trisomy 13 can be identified in a screening program for trisomy 21, based on a combinatio n of maternal age and fetal NT. (C) 1999 Wiley-Liss, Inc.