Fetal frontomaxillary facial angle in early pregnancy

Abstract

Introduction Trisomy 21 is the most common chromosomal abnormality and the single most common cause of intellectual disability. The work presented in this thesis investigates various aspects of frontomaxillary facial angle measurement as an additional ultrasound marker of trisomy 21 in first trimester screening. Methods Literature review of the frontomaxillary facial angle measurement technique revealed inexact and often contradictory fetal morphological landmarks and measurement protocols. In an effort to achieve a more reproducible and accurate measurement method, the frontomaxillary facial angle measurement technique was refined, stipulating strict morphological landmark identification and caliper placement criteria, prior to patient recruitment and data collection. The reproducibility of the methodology in both 2D and 3D imaging was formally tested and prospectively applied to various sub-populations in both euploid and aneuploidy fetuses. Results There is a learning curve associated with this technically challenging measurement but, with appropriate training and experience, frontomaxillary facial angle measurements in both 2D and 3D are equivalent and reliable, when strict image capture and volume acquisition protocols are followed. Caucasian fetuses were found to have larger frontomaxillary facial angle measurements compared to subgroups of Asian fetuses. Trisomy 21 fetuses had significantly larger frontomaxillary facial angle measurements in both 2D and 3D than euploid fetuses. Conclusion By following a strict measurement technique, experienced sonographers can accurately measure frontomaxillary facial angle utilizing both 2D and 3D ultrasound during routine first trimester aneuploidy screening without extending the length to the examination. Frontomaxillary facial angle is a reliable marker for trisomy 21 in the first trimester and could potentially be included in an aneuploidy risk assessment program.