These instruments consist basically of two crossing branches. Each branch has four components: blade, shank, lock, and handle. Each blade has two curves: the outward cephalic curve conforms to the round fetal head, and the upward pelvic curve corresponds more or less to the axis of the birth canal. Some varieties have an opening within or a depression along the blade surface and are termed fenestrated or pseudofenestrated, respectively (Fig. 29-2). These blade modifications permit a firmer grasp of the fetal head, but at the expense of increased blade thickness, which may increase vaginal trauma. In general, Simpson or Elliot forceps, with their fenestrated blades, are used to deliver a fetus with a molded head, as is common in nulliparous women. The Tucker-McLane forceps have thin smooth blades and are often used for a fetus with a rounded head, which is more characteristic in multiparas (Fig. 29-3). In most situations, however, any of these are appropriate.
Elliot forceps. A. Note the ample pelvic curve in the blades. B. The cephalic curve, which accommodates the fetal head, is evident in the articulated blades. The fenestrated blade and the overlapping shank in front of the English-style lock characterize these forceps.
Tucker–McLane forceps. The blade is solid, and the shank is narrow.
The blades are connected to the handles by shanks. The common method of articulation, the English lock, consists of a socket located on the shank at the junction with the handle, into which fits a socket similarly located on the opposite shank (see Fig. 29-3). A sliding lock is used in some forceps, such as Kielland forceps (Fig. 29-4).
Kielland forceps. The characteristic features are minimal pelvic curvature (A), sliding lock (B), and light weight.
Forceps 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 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. 29-5). 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. 29-6). 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 as described for the left blade. After positioning, the branches are articulated (Fig. 29-7). If the head is positioned in a left occiput anterior or right occiput anterior position, then the lower of the two blades is typically placed first.
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.
A. Continued insertion of the left blade. The right hand, not shown here, guides the blade during placement. Note the arc of the handles as they rotate to be applied to the mother’s left. B. First blade in place. An assistant’s hand can hold this handle in place as the second blade is applied.
The vertex is now occiput anterior, and the forceps are symmetrically placed and articulated.
The blades are constructed so that their cephalic curve is closely adapted to the sides of the fetal head. The biparietal diameter of the fetal head corresponds to the greatest distance between appropriately applied blades. Consequently, the fetal head is perfectly grasped only when the long axis of the blades corresponds to the occipitomental diameter. These diameters are depicted in Figure 7-12 (Central Nervous System and Spinal Cord). As a result, most of the blade lies over the face. If the fetus is in an occiput anterior position, then the concave arch of the blades is directed toward the sagittal suture. If the fetus is in an occiput posterior position, then the concave arch is directed toward the fetal face.
For the occiput anterior position, appropriately applied blades are equidistant from the sagittal suture, and each blade is equidistant from its adjacent lambdoidal suture. In the occiput posterior position, the blades are equidistant from the midline of the face and brow. Also for occiput posterior 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). For these reasons, the forceps must be applied directly to the sides of the fetal head along the occipitomental diameter.
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.
If necessary, rotation to occiput anterior is performed before traction is applied (Fig. 29-9). When it is certain that the blades are placed satisfactorily, then gentle, intermittent, horizontal traction is exerted concurrent with maternal efforts until the perineum begins to bulge (Fig. 29-10). 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 gradually elevated, eventually pointing almost directly upward as the parietal bones emerge (Figs. 29-11 and 29-12). As the handles are raised, the head is extended. During the birth of the head, spontaneous delivery should be simulated as closely as possible.
Forceps have been locked. Vertex is rotated from left occiput anterior to occiput anterior (arrow).
Occiput anterior. Delivery by low forceps. The direction of gentle traction for delivery of the head is indicated (arrow).
Upward arching traction (arrow) is used as the head is delivered.
Upward traction is continued as the head is delivered.
The force produced by the forceps on the fetal skull is a complex 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 advance of the head. If done, however, the thickness of the blades 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. 29-13). Importantly, if blades are disarticulated and removed too early, the head may recede and lead to a prolonged delivery. Pushing in some cases may be aided by addition of the modified Ritgen maneuver.
Forceps may be disarticulated as the head is delivered. Modified Ritgen maneuver may be used to complete delivery of the head.
Delivery of Occiput Posterior Positions
Prompt delivery may at times become necessary when the small occipital fontanel is directed toward one of the sacroiliac synchondroses, that is, in right occiput or left occiput posterior positions. When delivery is required in either instance, the head is often imperfectly flexed. In some cases, when the hand is introduced into the vagina to locate the posterior ear, the occiput rotates spontaneously toward the anterior, indicating that manual rotation of the fetal head might easily be accomplished.
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 in a right posterior position, rotation is clockwise to bring it to a right occiput anterior or to a straight occiput anterior position. With left occiput posterior position, rotation is counterclockwise. If resistance is met during rotation, the head may be slightly elevated but should not be disengaged, as this risks cord prolapse. After the occiput has reached the anterior position, labor may be allowed to continue, or forceps can be applied. Le Ray and colleagues (2007, 2013) reported a success rate of greater than 90 percent with manual rotation.
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 the occiput posterior position may be the safest procedure (Fig. 29-14). In many cases, the cause of the persistent occiput posterior position and of the difficulty in accomplishing rotation is an anthropoid pelvis. This architecture opposes rotation and predisposes to posterior delivery (Fig. 2-20, The four parent pelvic types of the Caldwell–Moloy classification).
Outlet forceps delivery from an occiput posterior position. The head should be flexed after the bregma passes under the symphysis.
With forceps delivery from an occiput posterior position, horizontal traction should be applied until the base of the nose is under the symphysis. The handles should then be slowly elevated until the occiput gradually emerges over the anterior margin of the perineum. Then, the forceps are directed in a downward motion, and the nose, mouth, and chin successively emerge from the vulva.
Occiput posterior delivery causes greater distention of the vulva, and a large episiotomy may be needed. Pearl and associates (1993) reviewed 564 occiput posterior deliveries and compared them with 1068 occiput anterior deliveries as controls. The occiput posterior group had a higher incidence of severe perineal lacerations and extensive episiotomy compared with the occiput anterior group. From The Netherlands, de Leeuw and associates (2008) studied more than 28,500 operative vaginal deliveries and reported similar findings. Consequences of these perineal tears are discussed in Chapter 27 (Route of Delivery). Also, infants delivered from the occiput posterior position had a higher incidence of Erb and facial nerve palsies, 1 and 2 percent, respectively, than did those delivered from the occiput anterior position. As expected, rotations to occiput anterior ultimately decrease perineal delivery trauma (Bradley, 2013).
For rotations from the occiput posterior position, Tucker-McLane, Simpson, or Kielland forceps may be used. The oblique occiput may be rotated 45 degrees to the posterior position, or 135 degrees to the anterior position. If rotation is performed with Tucker-McLane or Simpson forceps, the head must be flexed, but this is not necessary with Kielland forceps because they have a less pronounced pelvic curve. In rotating the occiput anteriorly with Tucker-McLane or Simpson forceps, the pelvic curvature, originally directed upward, is, at the completion of rotation, inverted and directed posteriorly. Attempted delivery with the instrument in this position is likely to cause vaginal sulcus tears and sidewall lacerations. To avoid such trauma, it is essential to remove and reapply the instrument as previously described for occiput anterior delivery.
Rotation from Occiput Transverse Positions
When the occiput is obliquely anterior, it gradually rotates spontaneously to the symphysis pubis as traction is exerted. When it is directly transverse, however, a rotary motion of the forceps is required. When the occiput is directed toward the patient’s left, rotation counterclockwise from the left side toward the midline is required. For right occiput transverse positions, clockwise rotation is required.
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. The latter have a sliding lock and almost no pelvic curve (see Fig. 29-4). On each handle is a small knob that indicates the direction of the occiput. The station of the fetal head must be accurately ascertained to be at, or preferably below, the level of the ischial spines, especially in the presence of extreme molding.
Kielland described two methods of applying the anterior blade. The first is the wandering or gliding method in which the anterior blade is introduced at the side of the pelvis over the brow or face. The blade is then arched around the brow or face to an anterior position, with the handle of the blade held close to the opposite maternal buttock throughout the maneuver. The second blade is introduced posteriorly and the branches are locked.
The second is the classic application in which the anterior blade is introduced first with its cephalic curve directed upward, curving under the symphysis. After it has been advanced far enough toward the upper vagina, it is turned on its axis through 180 degrees to adapt the cephalic curvature to the head. For a more detailed description of Kielland forceps procedures, see the second edition of Operative Obstetrics (Gilstrap, 2002).
Application of forceps to an occiput transverse positioned fetus in these women with a platypelloid pelvis should not be attempted until the fetal head has reached or approached the pelvic floor. Regardless of the original position of the head, after rotation, delivery eventually is accomplished by exerting traction downward until the occiput appears at the vulva. After this, the rest of the operation is completed as previously described for occiput anterior delivery.
Face Presentation Forceps Delivery
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.