Vacuum-assisted (instrumental) vaginal delivery

What it is

Instrumental delivery is vaginal delivery assisted by a vacuum, the ventouse, or by forceps. The most important landmark before instrumental delivery is the posterior fontanelle. Forceps carry the more morbidity of the two.

How it is treated

The fetal indication is fetal distress. The maternal indications are a prolonged 2nd stage of labour, maternal exhaustion, and the wish to shorten the 2nd stage in cardiac diseases, hypertensive crisis, proliferative retinopathy or myasthenia gravis. The 2nd stage is prolonged when a primigravida lacks continuing progress for 3hrs with regional anesthesia or 2hrs without, or a multigravida for 2hrs with regional anesthesia or 1hr without.

The pre-requisites spell FORCEP: fully dilated cervix, rotated head with the sagittal suture anteroposterior and the position either OA or OP, ruptured membrane, consent, absent cephalopelvic disproportion meaning no grade 3 molding, engaged head, and plus 2 station and beyond.

The vacuum is preferred in fetal distress. Forceps are preferred for the aftercoming head of breech, where Piper forceps are used, and for a dead fetus.

Correct application differs. The vacuum cup goes on the flexion point, which lies 3 cm in front of the posterior fontanelle or 6 cm behind the anterior fontanelle. Forceps blades sit at equal distance from the sagittal suture and lock easily, are applied in the occipito-mental diameter with the sagittal suture in the anterior-posterior position on PV examination, and a biparietal, bimalar application is the only safe application.

The vacuum comes as soft anterior cups, rigid anterior cups and rigid posterior cups; the Kiwi Omnicup is a rigid posterior cup used in the occipitoposterior position. Forceps are named by station: outlet forceps when the scalp is visible at the vulva without separating the labia (Wrigley's); low forceps with the vertex at +2 station and beyond (Simpson, Elliot); midforceps when the head is engaged but the leading point of the skull is above +2 station and the sagittal suture is not in AP position; Tucker Mclane for midforceps and outlet; Kielland for midforceps and rotation; and Piper for the aftercoming head of breech.