Assesment by Ultrasonography of the Perineal-cephalic Distance

The practice of ultrasounds increases in delivery rooms every year. Indeed, this method can help to visualize elements that may not be observable after clinical examination. Moreover, it is known that a fetal head engagement can lead to an instrumental extraction and in case of error, which happens in some cases, fetal and maternal risks are possible. These elements led to the investigators' hypothesis which is that a trans-perineal ultrasonography may facilitate the evaluation of a clinical fetal head engagement in case of doubt.