AbstractBackground4q21 microdeletion syndrome is an emergent non‐recurrent genomic disorder characterized by facial dysmorphy, progressive growth retardation, severe intellectual deficit, and absent or severely delayed speech. Deletions occur in clusters along 4q interstitial or terminal regions. 4q chromosomal aberrations are variable in type, size, and breakpoint. Genotype–phenotype correlation is a challenging task. The recurrent antenatal feature associated a posteriori with this syndrome is intrauterine growth retardation. There are very few precise antenatal descriptions of this syndrome.MethodsWe report here the first antenatal history of one of the largest deletion of this region.ResultsOur case harbored a 16.9 Mb deletion encompassing 135 protein coding genes including 20 OMIM morbid genes involved in neurological and cognitive abilities. Those breakpoints overlap two clusters of described microdeletion syndromes of cytogenetic band 4q13 and 4q21.ConclusionFrom the end of the second trimester, set of call signs associated with this syndrome can be completed by: excess of amniotic fluid, mild growth retardation, short long bones, bony anomalies of the extremities, and bulging cheeks. So, emphasis should be placed on the examination of the extremities, and the face during the routine targeted prenatal ultrasound.