Methods for prenatal screening for trisomy 21 employ examination of the fronto-maxillary facial (FMF) angle of a fetus. The methods may comprise obtaining a two or three dimensional image of a fetal face, measuring the FMFbone angle and/or FMFskin angle on the image, and comparing the measured FMFbone angle and/or FMFskin angle with an FMFbone angle and/or FMFskin angle characteristic of chromosomally normal fetuses. A measured FMFbone angle and/or FMFskin angle greater than the FMFbone angle and/or FMFskin angle characteristic of chromosomally normal fetuses provides an indication of an increased likelihood of the occurrence of trisomy 21 in the fetus.