Objective To determine the value of fetal Frontomaxillary facial angle (FMFA) in diagnosing chromosomal aneuploidy at 11+0-13+6 weeks of pregnancy. Methods Singleton pregnancies were randomly selected from January 2015 to August 2016 in our hospital. The crown-rump length (CRL), nuchal translucency (NT) and FMFA of the fetuses were measured and recorded, followed by chromosomal tests. FMFA and NT of the euploid fetuses were compared with those of the aneuploidy fetuses. A linear regression model was established between FMFA and CRL. The specificity and sensitivity of FMFA for diagnosing aneuploidy were assessed using the receiver operating characteristic (ROC) curve. Results The euploid fetuses had 80.61° (79.94°-81.28°) FMFA, compared with 91.24° (90.21°-92.25°) in the aneuploidy fetuses. The euploid fetuses had 1.63 mm (0.90-2.43 mm) NT, compared with 4.18 mm (3.12-5.44 mm) NT in the aneuploid fetuses. The differences were statistically significant (P<0.01). A negative correlation between CRL and FMFA was found in the euploid fetuses（y=－0.320 8x+100.32）. FMFA had a sensitivity of 90.5% and a specificity of 94.3% for diagnosing chromosomal aneuploidy with a cut-off value of 87.5° and 0.960 of the area under the curve. Conclusion Aneuploid fetuses have significantly greater FMFA than euploid fetuses at 11+0 to 13+6 weeks of gestation.
