Frontonasal facial angle in chromosomally normal fetuses at 11+0 to 13+6 weeks

Aim:  To establish the normal range of frontonasal angle (FNA) at 11+0 to 13+6 weeks of gestation and the feasibility of FNA measurement, evaluate the correlation of such a parameter with crown-rump length (CRL) and nuchal translucency (NT) and assess the potential of FNA in improving the performance of first trimester sonographic and biochemical screening for trisomy 21. Methods:  We conducted a prospective study in 400 singleton uncomplicated pregnancies. FNA was obtained during maternal screening for trisomy 21. NT thickness and FNA were measured by 2D ultrasound in a midsagittal plane of the fetal profile. FNA was measured between the line along the upper surface of the frontal bone and the superior edge of the nasal profile until the echogenic tip. Determination of maternal serum free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A) was committed and concomitantly evaluated by blood sample. Patient-specific risk was calculated using Fetal Medicine Foundation software (Astraia Software GMBH, Munich, Germany). Results:  Mean FNA increased with CRL from 119.80° at CRL 45 mm to 125.85° at CRL 84 mm. A significant association between the FNA and NT thickness was detected, while no significant association was found between FNA and serum PAPP-A or β-hCG. Conclusion:  At 11+0 to 13+6 weeks FNA increases with fetal CRL and NT thickness. Such an increase is not related to serum biochemistry.