Fetal micrognathia: almost always an ominous finding.

The fetal mandible is a common site for defects induced by a large number of genetic conditions and adverse environmental factors. Its complex development, described briefly below, requires several elements from different embryonic components to interact and fuse, both among themselves and with the cranial neural crest cells; this multistep process is highly susceptible to a series of molecular and genetic insults. These elements explain why an abnormal form of mandibular development, i.e. micrognathia, is a characteristic feature of a long list of chromosomal and non-chromosomal conditions, a good number of which are detectable in the fetus. A search for the word ‘micrognathia’ with no time limits in the OMIM website1, retrieved 363 hits. The conditions that can be associated with micrognathia and for which prenatal diagnosis is deemed feasible are reported in Tables 1–42.