P40.06: Absent nasal bones demonstrated with three‐dimensional maximum render mode in second‐trimester screening for Down syndrome

Abstract

Absent nasal bone has been described as a marker for Down Syndrome in the second trimester fetus. To check the real incidence of absent fetal nasal bones when visualized with 3D render mode. A prospective study was conducted in 1996 consecutive singleton pregnancies at 20–22 weeks' gestation. A detailed ultrasound examination, including fetal echocardiography (FE) and genetic scan (GS), were performed by three skilled gynecologists. Three-dimensional ultrasound of the fetal face, with maximum rendering mode, which highlights bones, was utilized to visualize and measure both nasal bones. In two cases absent nasal bones were demonstrated in fetuses with no other major structural anomalies detectable by ultrasound. Case I: A 27-year-old patient, gravida 1, was referred at 22 weeks' gestation. A detailed scan revealed absent nasal bones, brachycephaly, borderline pyelectasis (5 mm), very short humerus and short femur. An increased fetal risk for Down syndrome was discussed with the parents, that opted for amniocentesis. A Down syndrome diagnosis was confirmed. Case II: a 35-year-old woman, para 1 gravida 2, was referred for NT scan. The NT measured 2.8 mm, giving a risk for Down syndrome of 1: 50, the patient opted for amniocentesis, delayed at 19 weeks because of maternal recurrent flu. At 19 weeks + 6 days the scan showed normal fetal biometry, absent nasal bones, brachycephaly and two echogenic intracardiac focuses in the left heart ventricle. Amniocentesis result was positive for Down syndrome. In our experience bilateral absent fetal nasal bone, demonstrated with three-dimensional ultrasound of the fetal face, using maximum rendering mode, is a rare finding at 20–22 weeks' gestation. In our opinion, absent fetal nasal bones, when associated with fetal brachycephaly seems to be a strong marker of Down syndrome and fetal karyotype should be suggested.