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

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