[The fetal head: from screening to diagnosis].

The implementation of a prenatal screening ultrasound program to the general population requires a few rules. The sonographers must be adequately trained and the required imaging planes of the fetal head must be easy to acquire and be readily reproducible irrespective of the technology used. Screening for the presence of a potential local or global anomaly can be mainly established from a reference image. The diagnosis of an anomaly is confirmed from a different medical approach and is usually done during the second trimester (21 weeks GA).