Bilateral nasal bone measurements in normal first trimester fetuses and fetuses with trisomy 21 by use of 3D ultrasound

Purpose: Three-dimensional ultrasound with its different display modes allows an accurate demonstration of the ossified bones of the fetal face in the first trimester. In particular, the nasal bones can be evaluated on both sides and measured separately. The aim of this study was to establish the normal range for the left and right nasal bone and to demonstrate the development of the nasal bones in cases with trisomy 21 in the first trimester.

Material and method: In 200 normal fetuses and 12 fetuses with trisomy 21 the left and right nasal bone was measured in the multiplanar 3D mode after aligning the fetal head into an exact upright position to get a true profile. All scans were performed using E8/E10 GE equipment (Zipf, Austria) with a 5 – 8 MHz 3D abdominal or a 5 – 9 MHz 3D vaginal transducer. Gestational age was between 10+3 and 14+0 weeks of gestation.

Results: In the normal fetuses 151 cases had the same nasal bone length on both sides. In 43 cases a difference of up to 5 mm between the left and right nasal bone could be observed and in 3 cases even absence of the nasal bone on one side was found. In the 12 fetuses with trisomy 21, 3 cases showed bilateral hypoplasia of the nasal bones and 9 cases absence of nasal bones on both sides.

Conclusions: Three-dimensional ultrasound is a useful tool in the evaluation of the nasal bones in the first trimester. Because 23% of the normal cases showed a difference between the left and right nasal bone length, it is important to measure the nasal bone length on both sides consequently.