What is a key criterion for outlet forceps-assisted birth?

The key criterion for outlet forceps-assisted birth is that the fetal scalp is visible at the vaginal opening between contractions. This indicates that the fetal head has descended sufficiently into the birth canal and is in the optimal position for the use of forceps.

In outlet forceps-assisted birth, the visibility of the fetal scalp during contractions serves to confirm that the fetal head is engaged and that there is a need for assistance to facilitate delivery. This visibility also helps ensure the safety of both the mother and fetus during the procedure, as it provides a clear indication of the fetal head's position relative to the pelvic outlet.

While the fetal skull being above the pelvic floor indicates that engagement has not yet occurred, a bulging perineum suggests that the fetal head is low, and the fetal sagittal suture being at an angle greater than 45 degrees from midline can complicate the delivery. These factors do not align with the clinical definition of an outlet forceps delivery, which specifically requires the fetal scalp to be observable.