Frontomaxillary facial angle at 11 + 0 to 13 + 6 weeks in Chinese population

To establish the normal range of frontomaxillary facial (FMF) angle in the first trimester in a Chinese population.

In a prospective study from March 2007 to June 2007, three-dimensional (3D) volumes of the fetal profile in the mid-sagittal plane were recorded from 129 Chinese pregnant women who were screened for trisomy 21 by the combination of fetal nuchal translucency (NT) thickness, maternal serum free β-human chorionic gonadotropin (β-hCG) and pregnancy-associated plasma protein-A (PAPP-A) at 11 to 13 + 6 weeks. 3D volumes were examined using multiplanar techniques. The FMF angle of each case was measured. The relationship between the measured FMF angle with the other parameter was also examined.

The mean FMF angle decreased from 86.8 degree for a crown-rump length (CRL) of 45 mm to 76.0 degree for a CRL of 84 mm (FMF angle = 99.49 - 0.28 x CRL, r=0.377, p<0.0001). There was no significant association between the FMF angle with serum PAPP-A or β-hCG. The mean (SD) difference between FMF angle derived from Chinese formula and that from the published Caucasian equation was 1.47 (0.61) (95% CI 1.37-1.58) (p<0.0001).

In the first trimester, the FMF angle decreases with fetal CRL. There was similarity in the normal value of FMF angle between the Chinese and Caucasian populations.