Sonographic screening for trisomy 13 at 11 to 13(+6) weeks of gestation.

OBJECTIVE The purpose of this study was to examine the sonographic features of trisomy 13 at 11 to 13(+6) weeks of gestation. STUDY DESIGN This was a retrospective study that examined the features of trisomy 13 at the ultrasound scan at 11 to 13(+6) weeks of gestation, which in our center is performed for the measurement of crown-rump length, nuchal translucency thickness, and fetal heart rate and the examination for major defects. RESULTS In the 181 fetuses with trisomy 13, there were holoprosencephaly, exomphalos, and/or megacystis in 92 fetuses (50.2%), fetal heart rate above the 95th percentile in 129 fetuses (71.3%), and nuchal translucency above the 95th percentile in 141 fetuses (77.9%). There was no significant association between nuchal translucency and fetal heart rate, and it was estimated that inclusion of fetal heart rate in nuchal translucency screening can improve the detection rate of trisomy 13 by approximately 5%. CONCLUSION At the 11 to 13(+6)-week scan, the measurement of fetal nuchal translucency and fetal heart rate and fetal examination for holoprosencephaly, exomphalos, and megacystis can identify >90% of fetuses with trisomy 13.