Forceps blades grasp the head and are applied according to fetal head position. If the head is in an occiput anterior (OA) position, two or more fingers of the right hand are introduced inside the left posterior portion of the vulva and then into the vagina beside the fetal head. he handle of the left branch is grasped between the thumb and two fingers of the left hand (Fig. 29-4).
FIGURE 29-4 For OA or LOA positions, the left handle of the forceps is held in the left hand. The blade is introduced into the left side of the pelvis between the fetal head and the fingers of the operator's right hand.
FIGURE 29-5 Insertion arc of the blade. Importantly, the thumb of the right hand, guides the blade during placement, as shown in Figure 29-6.
he blade tip is then gently passed into the vagina between the fetal head and the palmar surface of the ingers of the right hand (Fig. 29-5). For application of the right blade, two or more ingers of the left hand are introduced into the right posterior portion of the vagina to serve as a guide for the right blade. his blade is held in the right hand and introduced into the vagina. With each blade, the thumb is positioned behind the heel, and most of the insertion force comes from this thumb (Fig. 29-6). If the head is positioned in a let OA (LOA) or right OA (ROA) position, then the lower of the two blades is typically placed irst. Mter positioning, the branches are articulated.
he blades are constructed so that their cephalic curve is closely adapted to the sides of the fetal head (Fig. 29-7). The fetal head is perfectly grasped only when the long axis of the blades corresponds to the occipitomental diameter (see Fig. 29-1). As a result, most of the blade lies over the lateral face. If the fetus is in an OA positi�n, then the concave arch of the blades is directed toward the sagittal suture. If the fetus is in an occiput posterior (OP) position, then the concave arch is directed toward the midline face.
Suboptimal blade placement can increase morbidity (Ramphul, 2015). For OA position, appropriately applied blades are equidistant from the sagittal suture, and each blade is equidistant from its adjacent lambdoidal suture. In the OP position, the blades are equidistant from the midline of the face and brow. Also for OP position, blades are symmetrically placed relative to the sagittal suture and each coronal suture. Applied in this way, the forceps should not slip, and traction may be applied most advantageously. With most forceps, if one blade is applied over the brow and the other over the occiput, the instrument cannot be locked, or if locked, the blades will slip of when traction is applied (Fig. 29-8).
With both branches in place, it should be an easy matter to articulate the handles, engage the lock, and correct asynclitism if present. Asynclitism is resolved by pulling and/or pushing each branch along the long axis of the instrument until the
FIGURE 29-6 In applying the second blade, insertional force is generated mainly by the thumb. (Reproduced with permission from Yeomans ER: Operative vaginal delivery. In Yeomans ER, Hoffman BL, Gilstrap LC III, et al (eds): Cunningham and Gilstrap's Operative Obstetrics, 3rd ed. New York, McGraw-Hili Education, 201•7.) inger guards align. If necessary, rotation to OA position is performed before traction is applied (Fig. 29-9).
When it is certain that the blades are placed satisfactorily, then gentle, intermittent, downward and outward traction is exerted concurrent with maternal eforts until the perineum