Proper traction necessary to avoid losing vacuum. Possible longer delivery than with forceps. Small increase in incidence of cephalohematomas. Ascertain that the cervix is fully dilated and the vertex is in low or outlet position. The vertex is then wiped clean, the labia are spread, and the cup is compressed and inserted.
Pressure is applied inward and downward until contact is made with the fetal scalp.
The cup should be placed over the posterior fontanelle. A finger is swept around the cup to make sure no maternal tissue is within the cup. Suction pressure is raised to 100 mm Hg, and the location of the cup is rechecked. With the onset of a contraction, suction pressure is raised to a range of 380 to 580 mm Hg. Traction is applied perpendicularly to the cup, in line with the maternal axis.