[Instrumental delivery with perineum-fetal head distance >55 MM on ultrasound].

Objective: Compare the issue of an operative vaginal delivery associated to the fetal presentation diagnosed by transperineal ultrasound. Three groups were formed: ≥55 mm, between 45 and 55 mm, and <45 mm.

Methods: A monocentric prospective study on 108 patients has been conducted between April 2011 and August 2014.