Retrospective 2D frontomaxillary facial angle measurements in trisomy 21 fetuses during routine first-trimester screening

Objective: The aim of this study is to assess the feasibility and utility of retrospective frontomaxillary facial angle measurement on two-dimensional (2D) images from confirmed trisomy 21 fetuses. Materials and methods: Over a 27-month period, stored 2D fetal profile images taken during routine first-trimester screening were assessed. A single experienced operator utilising an offline digital measurement tool measured the frontomaxillary facial angle of 55 karyotypically proven trisomy 21 fetuses. The resultant measurements were compared with 2D prospectively collected frontomaxillary facial angle measurements in both trisomy 21 and euploid fetuses, which were also performed by the same operator. Results: The mean maternal age of both trisomy 21 cohorts [37 years old (prospective) and 37.7 years old (retrospective)] was similar (p = 0.72), and both were greater than those of the euploid group (32.2 years old) (p<0.001). The median frontomaxillary facial angle measurement of the retrospective trisomy 21 cohort (90.5°) was greater than that of the euploid fetus group (87.1°) (p<0.001) but has no difference to the median of the measurements collected prospectively from trisomy 21 fetuses (91.1°) (p = 0.86). Conclusion: Overall, trisomy 21 fetuses have a larger frontomaxillary facial angle than euploid fetuses. Frontomaxillary facial angle measurements performed retrospectively in 2D were not different to prospective 2D frontomaxillary facial angle measurements.