Measurement of inferior facial angle and prefrontal space ratio in first trimester fetuses with aneuploidies: a retrospective study

: Objective To determine whether the measurement of inferior facial angle (IFA) and prefrontal space ratio (PFSR) in two-dimensional (2D) ultrasound images in the first trimester of pregnancy is reliable and to describe these markers in normal and aneuploid fetuses. Methods IFA and PFSR were measured in stored 2D midsagittal images of 200 normal and 140 aneuploid fetal profiles between 11 + 0 and 13 + 6 weeks of gestation. Limits of agreement (LOAs) and intraclass correlation coefficients (ICCs) for inter- and intraobserver differences were calculated. Results The mean IFA in normal fetuses was 76.5° ± 6.3. Between the two measurement rounds of the same observer, the LOAs were -5.4 to 7.1 (obs. 1) and 7.4 to 8.4 (obs. 2). For IFA measurements by the same observer the ICC was 0.88 (obs. 1) and for measurements by two different observers the ICC was 0.74. The mean PFSR was 0.76 ± 0.40 and the intraobserver LOAs were -0.372 to 0.395 (obs. 1) and -0.555 to 0.667 (obs. 2). For PFSR measurements by the same observer the ICC was 0.89 (obs. 1) and for measurements by two different observers the ICC was 0.65. Among aneuploid fetuses, IFA was below the normal range in one third of the cases with trisomy 18. PFSR was below the 95% prediction limit in 16.2% of fetuses with trisomy 21% and 17.9% of fetuses with trisomy 18. Conclusion IFA can be reliably measured in 2D ultrasound images in the first trimester of pregnancy with a high interobserver agreement and may provide information about retrognathia associated with various syndromes and aneuploidies at early stages of pregnancy.