Frontomaxillary Facial Angle Measurement in Trisomy 21 and Euploid Fetuses: Two- and Three-Dimensional Assessment during Routine First Trimester Screening

Abstract

Objective: To assess 2D and 3D frontomaxillary facial angle (FMFA) measurements in euploid and trisomy 21 fetuses. Materials and Methods: Over a 2-year period, women with singleton pregnancies attending a private prenatal screening and diagnosis practice in Sydney, Australia, were invited to participate in this study where 2D images and 3D volumes of the fetal face were collected during routine first trimester screening. In pregnancies where trisomy 21 was confirmed, FMFA measurements were performed in 2D and 3D and compared with those from a euploid cohort. Results: Overall, 250 women carrying euploid and 22 women carrying trisomy 21 fetuses participated. Trisomy 21 fetuses had significantly larger FMFA measurements than euploid fetuses in both 2D and 3D assessments. 95% of 3D and 100% of 2D FMFA measurements for the trisomy 21 fetuses were above the mean FMFA measurement of the euploid fetuses. There was no relationship between increasing crown-rump length and FMFA measurement. Conclusion: 2D and 3D FMFA measurements in trisomy 21 fetuses are statistically greater (p < 0.001) than those in euploid fetuses. This supports FMFA as a possible additional marker for trisomy 21 for first trimester screening.

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

“…We have shown that retrospectively collected data has similar patient age, fetal size and median frontomaxillary facial angle to the prospectively collected data, confirming the utility and accuracy of 2D retrospective frontomaxillary facial angle measurements performed on trisomy 21 fetuses, provided that the stored images are of sufficient quality and have appropriate anatomical landmarks for accurate caliper placement. Furthermore, the frontomaxillary facial angle measurements of trisomy 21 fetuses in retrospectively assessed 2D images are larger than those of the euploid fetuses, in accord with our findings in the prospectively collected trisomy 21 cohort and with the main body of literature …”

“…Figure 2B represents the overlaid caliper placement for frontomaxillary facial angle measurement. The data collected was then compared with the 2D prospective data collected by the same authors from trisomy 21 fetuses ( n = 22) and euploid fetuses ( n = 250).…”

“…However, in the instances where important departures from normality were found, non‐parametric tests were employed, including tests of medians, rank sum and Mann–Whitney's two‐sample tests. These tests were applied to the 2D trisomy 21 frontomaxillary facial angle retrospective data and the 2D trisomy 21 frontomaxillary facial angle prospective data collected during a previous study . Both the 2D retrospective trisomy 21 data and the 2D prospective trisomy 21 data were then compared with the median and 95% reference intervals for the frontomaxillary facial angle measurements of the euploid fetuses also collected in a previous study …”

“…These tests were applied to the 2D trisomy 21 frontomaxillary facial angle retrospective data and the 2D trisomy 21 frontomaxillary facial angle prospective data collected during a previous study. 17 Both the 2D retrospective trisomy 21 data and the 2D prospective trisomy 21 data were then compared with the median and 95% reference intervals for the frontomaxillary facial angle measurements of the euploid fetuses also collected in a previous study. 17 Ethics approval to measure the frontomaxillary facial angle on stored 2D images from fetuses confirmed to have trisomy 21 by karyotype was granted by The University of Sydney Human Research Ethics Committee (HREC 08-2008/11132).…”

“…Furthermore, the frontomaxillary facial angle measurements of trisomy 21 fetuses in retrospectively assessed 2D images are larger than those of the euploid fetuses, in accord with our findings in the prospectively collected trisomy 21 cohort and with the main body of literature. 9,17,[19][20][21] Frontomaxillary facial angle could be easily incorporated into the trisomy 21 risk factor algorithm in a contingent model for patients at 'intermediate risk' for trisomy 21, usually considered to be 1 in 100 to 1 in 1000, which occurs in approximately 10-15% of patients, with Nicolaides et al quoting 11%. 22 This allows modification of the risk, which would assist in the post-test counselling regarding early, definitive invasive testing by chorionic villus sampling or non-invasive prenatal testing if appropriate.…”