Operative Vaginal Delivery



Operative Vaginal Delivery


Michael A. Belfort



GENERAL PRINCIPLES



Definition



  • The use of forceps or vacuum extraction (VE) to facilitate delivery of the baby’s head during the second stage of labor







  • Forceps: Figure 4.4.1


  • Vacuum extractor: Figure 4.4.2


Physical Examination



  • Figure 4.4.3 shows the four parent types of maternal pelvis (Caldwell-Moloy classification).













  • Table 4.4.1 lists some important diameters of the maternal pelvis.


  • Performing clinical pelvimetry



    • Inlet



      • Can only be adequately evaluated before engagement of the fetal head because once the head occupies the midcavity, the posterior inlet cannot be accessed


      • Anteroposterior (AP) diameter



        • Diagonal conjugate = distance from the undersurface of the symphysis pubis to the sacral promontory


        • Obstetric conjugate (the narrowest AP diameter of the inlet) is estimated by subtracting 2 cm from the diagonal conjugate.


        • Transverse diameter of the inlet cannot be measured clinically.


        • The shape and the extent of the circumference of the inlet—sweep fingers laterally along the pelvic brim. If greater than two-thirds of the brim and/or posterior portions of the brim can be felt = contracted inlet.


    • Midcavity (midpelvis)



      • Shape of the sacrum (curved or straight)


      • Width of the sacrosciatic notch


      • Prominence of, and distance between, the ischial spines


      • A contracted midpelvis characteristically shows a flattened forward-projecting sacrum, prominent ischial spines with a narrowed interspinous distance, and a shortened sacrospinous ligament that is less than two fingerbreadths long.










    • Outlet



      • Distance between the ischial tuberosities (normally ˜10 cm)


      • Palpate coccyx: Normally mobile/not protruding into the pelvic cavity


      • Subpubic angle (normal > 90 degrees)


      • Retropubic angle (flattened in a platypelloid pelvis and sharply angulated in an android pelvis)


      • Convergence or divergence of the pelvic sidewalls (Figure 4.4.3).


  • During labor, for a complete picture of the situation clinical pelvimetry should be combined with fetal parameters such as the following:



    • Head position, molding, caput succedaneum, asynclitism, maternal and fetal soft-tissue edema, presence of meconium, and descent of the head


    • Fetal heart rate response to contractions and/or pushing.


  • Some important definitions are shown in Table 4.4.2:



    • American College of Obstetricians and Gynecologists (ACOG) (1) Classification of Station: Level of the leading bony point of the fetal head in centimeters at or below the level of the maternal ischial spines (-0 cm to +5 cm)


  • Applied fetal cephalic anatomy (2)



    • Figure 4.4.4 shows important landmarks.


    • Figure 4.4.5 presents relevant diameters of the fetal skull.


    • Table 4.4.3 shows the diameters and circumferences of the fetal head that will need to negotiate the maternal pelvis in specific fetal head positions.














  • Swellings seen on the neonate’s head (2):



    • Figure 4.4.6 shows types of swelling that may be seen on the neonatal head:



      • Caput succedaneum: Serous effusion between aponeurosis and periosteum overlying the leading part of the skull. Normal occurrence, from pressure from the cervix. There are varying degrees described subsequently. Usually disappears within hours of birth.















    • Caput succedaneum should be differentiated from the following two life-threatening bleeding differential diagnoses:



      • Cephalohematoma: Collection of blood between periosteum and skull bone, limited by periosteal attachments at the suture lines. Can still be significant. Takes hours to develop and weeks to reabsorb.







      • Subgaleal (subaponeurotic) hematoma: Potential space between galea aponeurotica (epicranial aponeurosis) and periosteum (pericranium). No boundaries—may extend from the orbital ridges to the nape of the neck with possibility of life-threatening hemorrhage. Presents with diffuse swelling of the head and signs of hypovolemic shock (e.g., pallor, hypotension, tachycardia, and increased respiration rate). The signs may be present at delivery or develop several hours or up to a few days following delivery. The swelling shifts dependently and indents easily on palpation. May be difficult to distinguish from the edema of the scalp, but any hypotension and pallor after an operative vaginal delivery (OVD) should be regarded as potential signs of a subgaleal bleed.


    • Molding: Molding is an expected deformation of the fetal head that occurs during the delivery process. A small amount of occipitoparietal molding is normal during the second stage, but excessive skull bone molding (particularly parietoparietal molding) is abnormal during the first stage of labor. Molding can be classified in the following way (Figure 4.4.7) (2,3,4,5):









      • 0+ = suture easily felt between the two bones


      • 1+ = no suture felt, bones easily separated by minimal digital pressure


      • 2+ = overlapping bones, separated with digital pressure


      • 3+ = overlapping bones, cannot be separated with digital pressure


  • Fetal head position



    • It is axiomatic that until the exact head position and station are known, OVD should not be attempted.


    • If necessary, ultrasound can be used to confirm clinical findings, either translabially or transabdominally (6).


  • Abdominal examination



    • Routine assessment before OVD to confirm the lie and identify relationship of fetal back to the uterine midline



      • If fetal back is not felt, or is palpated laterally, there is a higher likelihood of the baby being in an occipitoposterior or transverse position.


      • Assess fetal weight.


      • Assess amount of fetal head (in “fifths”) palpated above the pelvic brim (Figure 4.4.8) (3,4,5).



        • The average adult hand is ˜10 cm across from thumb to little finger. Thus, each finger is ˜2 cm in width, or one-fifth of the hand. Using the number of fingerbreadths of the fetal head palpated above the maternal symphysis, an estimation on the “number of fifths” of the fetal head can be made.


        • If greater than two-fifths of the fetal head (two fingerbreadths) is palpable above the pubic symphysis, regardless of the fact that the scalp is felt at the ischial spines, the head should be regarded as unengaged and an operative delivery should be avoided.


    • Rule of three’s (3,4,5)



      • See Figure 4.4.9. If the sum of the number of fifths of the fetal head felt above the pubic symphysis and the degree of molding is ≥3, then OVD is contraindicated (3,4,5).


    • Value of the abdominal examination (5)



      • Prediction of successful OVD has been studied and shown to be better when using abdominal examination criteria (including an assessment of the amount of fetal head palpated above the pubic symphysis) (94%) than by vaginal examination criteria (80%) (p < 0.01).


IMAGING AND OTHER DIAGNOSTICS



  • Pelvic x-ray



    • No longer employed except in low-resource environments where ultrasound and/or magnetic resonance imaging (MRI)
      is not available. X-ray pelvimetry may be useful in such environments to rule out pelvic abnormalities.







  • Ultrasound (6)



    • May be useful to determine fetal size, presentation, position, station, and viability in labor












    • May be useful to diagnose head position just before OVD (Figure 4.4.10) (6)


  • MRI scan



    • May be useful for pelvimetry or for diagnosing fetal anomalies in well-resourced environments



PREOPERATIVE PLANNING



  • Prerequisites for OVD



    • Table 4.4.4 presents a mnemonic that is useful in ensuring the best chance of success for an OVD.


    • Contraindications to OVD (Table 4.4.5)


  • Preoperative note



    • Recommended in all but emergent circumstances
















    • Document indication (Table 4.4.6) and satisfied prerequisites (Table 4.4.4) and expected type (Table 4.4.7) of OVD, as well as the fact that risks and benefits were discussed, assent or informed consent given, and the alternative of a cesarean section offered and declined. Patients should be informed of the risk of intracranial hemorrhage and neonatal intensive care unit (NICU) admission—Towner et al. (7) provide useful population-based information showing a similar risk of intracranial bleeding following OVD versus cesarean birth after prolonged labor. The reader is encouraged to read the Towner et al. paper to become familiar with the increased relative risk of OVD under various circumstances such as failed OVD and sequential use of OVD instruments.


  • Analgesia



    • Regional block: Epidural or spinal conduction anesthesia is optimal.


    • Pudendal block and perineal infiltration if regional is not possible.


    • General anesthesia may be indicated under individualized circumstances.


  • “Ghosting”



    • Assembling the forceps or vacuum extractor before use


    • Check that all parts fit together and function well.


    • Held in a way that simulates the intended application and use


  • Prophylactic antibiotics



    • Mediolateral episiotomy—recommended by ACOG (1)


    • Median episiotomy—not recommended by ACOG (1)


SURGICAL MANAGEMENT


Positioning



  • Modified lithotomy position



    • In special cases (such as cardiac disease), this should be modified with the patient in a Fowler position with their feet on small stools below the level of the hips.