Fetal nasal bone: Review of first trimester findings

Abstract

In 1866, Langdon Down included in his observation of individuals with the syndrome that would come to bear his name the following statements: ‘‘The nose is small. The face is flat and broad, and destitute of prominence’’ [1]. The prenatal diagnosis involves an invasive procedure, which carries a 1% risk of fetal loss [2]. Since every woman has a risk of this form of aneuploidy, extensive research has been done to identify markers that would identify fetuses at risk of having this condition. The phenotypic appearance of a small nose, which may range from a complete absence of the nasal bone to diminished nasal bone length, has been seen during the prenatal period. There is a hope that the evaluation of the fetal nasal bone (NB) can add to our armamentarium and allow us to increase our sensitivity for detecting Down syndrome (trisomy 21) and ultimately limit the number of women who need an invasive procedure. It has now become possible to delineate the risk of trisomy 21 based on an evaluation of NB between 11 and 14 weeks [3–5]. The association between the absent NB seen on ultrasound and trisomy 21 was observed in a review of videotape recordings of first-trimester ultrasounds of three fetuses with trisomy 21 which showed absence of or small NB 2/3 fetuses [6]. Afterwards, in a prospective study of 701 fetuses, absent NB was found in 43/59 (73%) fetuses with trisomy 21, compared to 21/603 (0.5%) euploid fetuses. This association between trisomy 21 and absent NB was seen in a smaller study where the nasal bone was absent in 3/5 (60%) fetuses with trisomy 21 compared to 1/175 (0.6%) fetuses with normal chromosomes [7]. Larger studies came out later that demonstrated the effectiveness of using the absent nasal bone in the first trimester. A study of 5525 fetuses found absent NB in 70% of trisomy 21 fetuses compared with 0.5% of fetuses with normal fetuses [8]. In their latest assessment of the absent fetal nasal bone in a multiethnic population of 3788, Cicero et al. found an absent nasal bone in 161/242 (66.9%) of trisomy 21 fetuses compared to 93/3358 (2.3%) of fetuses