Outcome of Pregnancies with Isolated Absent Fetal Nasal Bone in the Second Trimester

Abstract

Absent nasal bone is associated with 58 genetic syndromes, Trisomy 18 and trisomy 21. It increases the sensitivity of second trimester scan for aneuploidy from 83 to 90%. Since 2003, absent or unossified nasal bone is therefore an integral part of the second trimester scan. The present study aimed at confirming the sensitivity of isolated absent NB in the second trimester USG, by reviewing the karyotypes and/or postnatal outcomes of such pregnancies up till at least 6 months of postnatal life. Facial profile was seen in 2D and 3D reconstructed view in all the cases to avoid missing the unilateral absence of nasal bone. Complete detailed scan and FISH on amniotic fluid cells was advised for all the cases with absent nasal bone. The present study concluded that isolated absence of NB in the second trimester may not be an effective marker for diagnosis of Down's syndrome. Amniocentesis should be advised only if absent nasal bone is associated with any other structural abnormality or additional soft marker.

Absent or hypoplastic nasal bone: What to tell the prospective parents?

“…Consequently, it is far more practical to perform a thorough scan at around 16 weeks to look for soft signs other than AHNB, and then to prioritize the woman for intrusive testing. Numerous studies have proposed a similar methodology (Benacerraf et al, 2019; Desai et al, 2019; Zhang et al, 2021) Adhering to this strategy in low‐resource situations will lower costs and the number of invasive treatments performed. However, when doing invasive testing, the sample should be sent for a more detailed analysis of the genomic structure of the fetus, like the microarray, over the conventional karyotype, as has been outlined in several studies (Fantasia et al, 2020; Gu et al, 2019; Shi et al, 2022; Zhang et al, 2021).…”