Forceps refers to the paired instrument, and each member of this pair is called a branch. Branches are designated left or right according to the side of the maternal pelvis to which they are applied (Fig. 29-2). Each branch has four components: blade, shank, lock, and handle (Fig. 29-3). Each blade has a toe, a heel, and two curves. Of these, the outward cephalic curve conforms to the round fetal head, whereas the upward pelvic curve corresponds more or less to the curve of the birth canal. Some blades have an opening within or a depression along the blade surface and are termed fenestrated or pseudofenestrated, respectively. True fenestration reduces the degree of head slippage during forceps rotation. Disadvantageously, it can increase friction between the blade and vaginal wall. With pseudofenestration, the forceps blade is smooth on the outer maternal side but indented on the inner fetal surface. The goal is to reduce head slipping yet improve the ease and safety of application and removal of forceps compared with pure fenestrated blades. In general, fenestrated blades are used for a fetus with a molded head or for rotation. In most situations, however, despite these subtle differences any are appropriate.
Simpson forceps have fenestrated blades, parallel shanks, and English lock. The cephalic curve accommodates the fetal head.
Luikart forceps have pseudofenestrated blades, overlapping shanks, sliding lock, tongue groove handles. The pelvic curve is marked in this example by the black line.
The blades are connected to shanks, which may be parallel or overlapping. Locks are found on all forceps and help to connect the right and left branches and stabilize the instrument. They can be located at the end of the shank nearest to the handles (English lock), at the ends of the handles (pivot lock), or along the shank (sliding lock). Although varied in design, handles, when squeezed, raise compression forces against the fetal head. Thus, forces to consider include traction and compression.
Blade Application and Delivery
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. The handle of the left branch is grasped between the thumb and two fingers of the left hand (Fig. 29-4). The blade tip is then gently passed into the vagina between the fetal head and the palmar surface of the fingers of the right hand (Fig. 29-5). For application of the right blade, two or more fingers of the left hand are introduced into the right posterior portion of the vagina to serve as a guide for the right blade. This 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 left OA (LOA) or right OA (ROA) position, then the lower of the two blades is typically placed first. After positioning, the branches are articulated.
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.
Insertion arc of the blade. Importantly, the thumb of the right hand, guides the blade during placement, as shown in 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-Hill Education, 2017.)
The 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 position, 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.
A. The forceps are symmetrically placed and articulated. B. The vertex is OA. (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-Hill Education, 2017.)
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 off when traction is applied (Fig. 29-8).
Incorrect application of forceps. A. One blade over the occiput and the other over the brow. Forceps cannot be locked. B. With incorrect placement, blades tend to slip off with traction.
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 finger guards align. If necessary, rotation to OA position is performed before traction is applied (Fig. 29-9).
A. If LOA, the vertex is rotated (arrow) from this position to OA (B). (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-Hill Education, 2017.)
When it is certain that the blades are placed satisfactorily, then gentle, intermittent, downward and outward traction is exerted concurrent with maternal efforts until the perineum begins to bulge. When the head is at 0 to +2 of +5 station, the initial direction of traction is quite posterior, almost toward the floor. With head descent, the vector of forces changes continuously (Fig. 29-10). As a teaching tool for this, a Bill axis traction device can be attached over the finger guards of most forceps. The instrument has an arrow and indicator line. When the arrow points directly to the line, traction is along the path of least resistance. With traction, as the vulva is distended by the occiput, an episiotomy may be performed if indicated. Additional horizontal traction is applied, and the handles are then gradually elevated. As the handles are raised, the head is extended. During the birth of the head, mechanisms of spontaneous delivery should be simulated as closely as possible.
With low forceps, the direction of gentle traction for delivery of the head is indicated (arrow). The vector changes with fetal descent.
The force produced by the forceps on the fetal skull is a function of both traction and compression by the forceps, as well as friction produced by maternal tissues. It is impossible to ascertain the amount of force exerted by forceps for an individual patient. Traction should therefore be intermittent, and the head should be allowed to recede between contractions, as in spontaneous labor. Except when urgently indicated, as in severe fetal bradycardia, delivery should be sufficiently slow, deliberate, and gentle to prevent undue head compression. It is preferable to apply traction only with each uterine contraction. Maternal pushing will augment these efforts.
After the vulva has been well distended by the head, the delivery may be completed in several ways. Some clinicians keep the forceps in place to control the head. If this is done, however, the blade volume adds to vulvar distention, thus increasing the likelihood of laceration or necessitating a large episiotomy. To prevent this, the forceps may be removed, and delivery is then completed by maternal pushing (Fig. 29-11). Importantly, if blades are disarticulated and removed too early, the head may recede and lead to a prolonged delivery. Delivery in some cases may be aided by addition of the modified Ritgen maneuver.
Branches are removed in the opposite order from that in which they were originally placed. The fingers of the right hand, covered by a sterile towel, bolster the perineum. The thumb is placed directly on the head to prevent sudden egress. (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-Hill Education, 2017.)
Occiput Posterior Positions
Prompt delivery may at times become necessary when the small occipital fontanel is directed toward one of the sacroiliac synchondroses. In these right OP (ROP) or left OP (LOP) positions, the fetal head is often imperfectly flexed. With OP positions, second-stage labor can be lengthened. In these cases, the head may spontaneously deliver OP, may be manually or instrumentally rotated to an OA position, or may be delivered OP by forceps or vacuum.
With manual rotation, an open hand is inserted into the vagina. The palm straddles the sagittal suture of the fetal head. The operator’s fingers wrap around one side of the fetal face and thumb extends along the other side. If the occiput is ROP, rotation is clockwise to bring it to an ROA or OA position (Fig. 29-12). With LOP position, rotation is counterclockwise. Three actions are performed simultaneously between contractions. The first is fetal head flexion to provide a smaller diameter for rotation and subsequent descent. Second, slight destationing of the fetal head moves the head to a level in the maternal pelvis with sufficient room to complete the rotation. Importantly, destationing should not be confused with disengaging the fetal head, which is proscribed. Concurrently, some prefer to also place the other hand externally on the corresponding side of the maternal abdomen to pull the fetal back up toward the midline in synchrony with the internal rotation. Le Ray and colleagues (2007, 2013) reported a success rate of greater than 90 percent with manual rotation. Barth (2015) provides an excellent summary of this technique.
A. Manual rotation using the left hand, palm-up, to rotate from ROP. B. The head is flexed and destationed during clockwise rotation to reach an OA position. (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-Hill Education, 2017.)
Manual rotations are most easily completed in multiparas. If manual rotation cannot be easily accomplished, application of forceps blades to the head in the posterior position and delivery from an OP position may be the safest procedure. In many cases, the cause of a persistent OP position and of the difficulty in accomplishing rotation is an anthropoid pelvis. This architecture opposes rotation and predisposes to posterior delivery (Fig. 2-17).
With forceps delivery from an OP position, downward and outward traction is applied until the base of the nose passes under the symphysis (Fig. 29-13). The handles are then slowly elevated until the occiput gradually emerges over the upper margin of the perineum. The forceps are directed downward again, and the nose, mouth, and chin successively emerge from the vulva.
Outlet forceps delivery from an OP position. The head should be flexed after the bregma passes under the symphysis.
OP delivery causes greater distention of the vulva, and a large episiotomy may be needed. OP deliveries have a higher incidence of severe perineal lacerations and extensive episiotomy compared with OA positions (de Leeuw, 2008; Pearl, 1993). Also, newborns delivered from OP positions have a higher incidence of Erb and facial nerve palsies, 1 and 2 percent, respectively, than those delivered from OA positions. As expected, rotations to OA ultimately decrease perineal delivery trauma (Bradley, 2013).
Last, for forceps rotations from an OP to OA position, the Kielland instruments are preferred because they have a less pronounced pelvic curve (Fig. 29-14). Cunningham and Gilstrap’s Operative Obstetrics, 3rd edition, offers a more detailed description of this Kielland forceps procedure (Yeomans, 2017).
Kielland forceps. The characteristic features are minimal pelvic curvature (A), sliding lock (B), and light weight.
Occiput Transverse Positions
With occiput transverse (OT) positions, rotation is required for delivery. With experienced operators, high success rates with minimal maternal morbidity can be achieved (Burke, 2012; Stock, 2013). Either standard forceps, such as Simpson, or specialized forceps, such as Kielland, are employed. With Kielland forceps, each handle has a small knob, and branches are placed so that this knob faces the occiput. The station of the fetal head must be accurately determined to be at, or preferably below, the level of the ischial spines, especially in the presence of extreme molding.
A. Application of the right branch of the Kielland forceps to a head in LOT position. The knob on this branch (colored blue) will ultimately face the occiput. B. The right branch is wandered to its final position behind the symphysis. C. Insertion of the left branch of the Kielland forceps directly posterior along the hollow of the sacrum. This branch is inserted to the maternal right of the anterior branch to aid in engaging the sliding lock. (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-Hill Education, 2017.)
Kielland described two methods of applying the anterior blade. In our example, placement with a left OT (LOT) position is described. With the wandering method, the anterior blade is first introduced into the posterior pelvis (Fig. 29-15). The blade is then arched around the face to an anterior position. To permit this sweep of the blade, the handle is held close to the maternal left buttock throughout the maneuver. The second blade is introduced directly posteriorly, and the branches are locked.
After checking the application, the handles of the Kielland forceps are pulled slightly to the patient’s right to increase fetal head flexion and create a smaller diameter for rotation. The first and second fingers of the left hand are placed over the finger guards with the palm against the handles. This palm faces the maternal left. Concurrently, the first two fingers of the operator’s right hand are placed against the anterior lambdoid suture. The fetal head is then destationed approximately 1 cm. For rotation in a counterclockwise direction, the wrist of the left hand supinates, to direct this palm upward. Simultaneously, two fingers of the right hand press on the edge of the right parietal bone that borders the lambdoid suture. This ensures that the fetal head turns with the blades and does not slip.
The second type of blade application introduces the anterior blade with its cephalic curve directed upward to curve under the symphysis. After it has been advanced far enough toward the upper vagina, it is turned on its long axis through 180 degrees to adapt the cephalic curvature to the head.
With either application, after rotation completion, the operator may choose from two acceptable methods for delivery. In one, the operator applies traction on the Kielland forceps using a bimanual grip described previously for conventional forceps (Forceps Delivery). When the posterior fontanel has passed under the subpubic arch, the handles can be elevated to the horizontal. Raising the handles above the horizontal may cause vaginal sulcus tears because of the reverse pelvic curve (Dennen, 1955). Alternatively, the Kielland forceps can be removed after rotation and replaced with conventional forceps. With this approach, moderate traction is first employed to seat the head before switching instruments.
With a mentum anterior face presentation, forceps can be used to effect vaginal delivery. The blades are applied to the sides of the head along the occipitomental diameter, with the pelvic curve directed toward the neck. Downward traction is exerted until the chin appears under the symphysis. Then, by an upward movement, the face is slowly extracted, with the nose, eyes, brow, and occiput appearing in succession over the anterior margin of the perineum. Forceps should not be applied to the mentum posterior presentation because vaginal delivery is impossible except in very small fetuses.