First-trimester assessment of nasal bone using retronasal triangle view: a prospective study

Area of Science:

• Obstetrics and Gynecology
• Fetal Medicine
• Medical Imaging

Background:

• First-trimester aneuploidy screening is crucial for early detection of chromosomal abnormalities.
• Fetal nasal bone (NB) assessment is a recognized marker for trisomy 21.
• The retronasal triangle (RNT) view offers a novel approach to NB visualization.

Purpose of the Study:

• To evaluate the feasibility and accuracy of using the RNT view for fetal NB assessment.
• To determine the effectiveness of NB assessment in the RNT view for first-trimester aneuploidy screening.
• To compare the performance of the RNT view with established methods for NB assessment.

Main Methods:

• Prospective evaluation of consecutive singleton pregnancies undergoing sonographic screening at 11-13 weeks' gestation.
• Attempted assessment of fetal NB using the RNT view, classifying it as present or absent/hypoplastic.
• Calculation of the detection rate for fetal karyotypic abnormalities based on NB assessment in the RNT view.

Main Results:

• The RNT view was successfully examined in 1970 out of 1977 fetuses (99.6%).
• Aneuploidy was detected in 39 cases (2.2%), with trisomy 21 being the most common (n=17).
• The prevalence of absent/hypoplastic NB was 70.6% in trisomy 21 cases versus 0.7% in normal fetuses, yielding a sensitivity of 70.6% and specificity of 99.3% for trisomy 21.

Conclusions:

• The RNT view is a feasible and effective technique for assessing the fetal nasal bone in the first trimester.
• Absent or hypoplastic nasal bone visualized via the RNT view is a significant marker for aneuploidy, especially trisomy 21.
• This approach demonstrates performance comparable to the mid-sagittal plane for NB assessment in aneuploidy screening.