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

Objective To establish the normal range of the fronto-maxillary facial (FM-F) angle at 11 + 0 to 13 + 6 weeks of gestation. Methods In this prospective study, three-dimensional (3D) volumes of the fetal head were obtained from 500 pregnancies before fetal karyotyping by chorionic villus sampling (CVS), after screening by fetal nuchal translucency (NT) thickness and maternal serum free beta-human chorionic gonadotropin (beta-hCG) and pregnancy-associated plasma protein-A (PAPP-A) at 11 + 0 to 13 + 6 weeks. Only cases with a normal karyotype were included in this study. The FMF angle was measured off-line. In a subgroup of 150 cases the FMF angle was measured using 2D ultrasound before obtaining a 3D volume. In 50 cases the 3D volumes were used to measure the FMF angle by the same examiner twice and by another examiner once. Results The mean FMF angle decreased with crown-rump length (CRL) from 84.3 degrees at CRL 45 mm to 76.5 degrees at CRL 84 mm. There was no significant association between the FMF angle and fetal NT or serum PAPP-A or beta-hCG. In the volumes with paired measurements, the difference between two measurements by the same or two sonographers was <5% in 95% of the cases. In the cases with paired 3D and 2D ultrasound measurements, the difference in FMF angles was <8% in 95% of the cases. Conclusions At 11 + 0 to 13 + 6 weeks the IMF angle decreases with fetal CRL but is not related to fetal NT or serum biochemistry. The measurement is reproducible and the results obtained by 3D and 2D ultrasound are similar.