Labor and Vaginal Delivery

VI LABOR, DELIVERY, AND POSTPARTUM

LABOR AND VAGINAL DELIVERY

Kelly A. Best, MD CHAPTER 61

1. What is the definition of labor? Labor begins when uterine contractions of sufficient frequency, intensity, and duration are attained to bring about effacement and progressive dilation of the cervix. 2. What two steps are theorized to be crucial to the initiation of labor in human pregnancy? 1. Retreat from pregnancy maintenance 2. Uterotonic induction Despite extensive investigation into the associated physiologic and biochemical changes, the physiologic processes in human pregnancy that result in the onset of labor are still not defined. 3. In which patients is induction of labor considered? Awaiting the onset of normal labor may not be an option in certain circumstances. At preterm gestations, indications for labor induction include severe preeclampsia, fetal growth restriction with abnormal antepartum surveillance or other evidence of fetal compromise, and deterioration of maternal disease to the point that continuation of pregnancy is believed to be detrimental. In cases of rupture of membranes without labor (i.e., premature rupture of membranes) at term (37 to 42 weeks) or postterm (≥42 weeks), induction of labor is often performed. 4. What is a Bishop score, and how is it used? A Bishop score is a quantifiable method to assess the likelihood of a successful induction. Elements include dilation, effacement, station, consistency, and position of the cervix (Table 61-1). A score of 6 or less trans- lates into a need to ripen the cervix and is associated with less successful inductions. A score 8 or greater generally means the cervix does not need ripening and induction is more likely to be successful.

Table 61-1. Bishop Scoring System for Assessment of Inducibility DILATION EFFACEMENT STATION CERVICAL CERVICAL SCORE (cm) (%) (-3 TO +3 SCALE) CONSISTENCY POSITION 0 Closed 0-30 −3 Firm Posterior 1 1-2 40-50 −2 Medium Midposition 2 3-4 60-70 −1, 0 Soft Anterior 3 ≥5 ≥80 +1, +2 — —

5. What methods are available for cervical ripening? Mechanical methods provide local pressure and stimulate endogenous release of prostaglandins, which results in cervical ripening. Options include a transcervical Foley catheter (filled with 30 to 60 mL after insertion) or hydroscopic dilators (laminaria or a similar synthetic product). Pharmacologic methods include low-dose oxytocin, prostaglandin E2 (dinoprostone), and prostaglandin E1 (misoprostol). Prostaglandin E1 can be administered intravaginally or orally, and prostaglandin E2 can be applied within the vagina in either gel or suppository form. 6. When is cervical ripening contraindicated? Contraindications to labor induction are the same as those for spontaneous labor and vaginal delivery. They include—but are not limited to—vasa previa, placenta previa, fetal malpresentation (e.g., breech 263 Downloaded for Sean Oldroyd ([email protected]) at KAWEAH DELTA MEDICAL CENTER from ClinicalKey.com by Elsevier on February 09, 2021. For personal use only. No other uses without permission. Copyright ©2021. Elsevier Inc. All rights reserved. 264 LABOR, DELIVERY, AND POSTPARTUM

or transverse lie), umbilical cord prolapse, and previous transfundal uterine surgical procedures. Because of an increased risk of uterine rupture during induction of labor with prostaglandins among women with previous low-transverse cesarean sections, the American College of Obstetricians and Gynecologists (ACOG) advises against the use of prostaglandins in these cases. For more information on a trial of labor after cesarean section (TOLAC), see Chapter 63. 7. How is the pelvis assessed clinically? Historically, clinical assessment of the pelvis (known as pelvimetry) was used to predict whether vaginal birth was possible and provide information about a patient’s overall pelvic dimensions and configuration. However, this has been shown not to be reliable; the best way to assess whether a pelvis is adequate is to allow for a trial of labor. • The pelvic inlet is bounded in the anteroposterior dimension (obstetric conjugate) by the sacral promontory and the pubic symphysis. Laterally, it is bound by the linea terminalis. The size of the pelvic inlet can be estimated by palpating the sacral promontory, which provides the measurement for the diagonal conjugate, which is approximately 1.5 to 2 cm greater than the obstetric conjugate. • The pelvic midplane is bounded laterally by the inferior margins of the ischial spines, anteriorly by the lower margin of the symphysis pubis, and posteriorly by the sacrum (usually S4 or S5). • The pelvic outlet consists of two triangular areas that are not in the same plane but share a common base, which is the distance between the two ischial tuberosities. The apex of the posterior triangle is at the tip of the sacrum, and the anterior triangle is formed by the area under the pubic arch (Fig. 61-1). Most patients have an intermediate form of the four classically described pelvic types (Fig. 61-2). 8. What are the three stages of labor? The first stage begins with the onset of labor and ends when the cervix is fully dilated (10 cm). The second stage begins when dilation of the cervix is complete and ends with delivery of the infant. The third stage begins immediately after delivery of the infant and ends with delivery of the placenta.

9. How are uterine contractions monitored? Uterine monitoring can be either external or internal. • External monitoring: performed by securing a displacement transducer to the maternal abdomen. When the uterus contracts, the transducer moves; this movement is translated into an electronic signal and is transcribed as a vertical displacement from the resting uterine tone. This form of monitoring provides information only about the frequency of contractions.

Transverse diameter (bituberous) Ant. triangle

Sacrotuberous Post. triangle ligt. Figure 61-1. The pelvic outlet. Ant., Anterior; ligt., ligament; post., posterior. (From Hobel CJ, Chang AB. Normal labor, delivery, and postpartum care. In: Hacker NF, Moore JG, Gambone JC, eds. Essentials of Obstetrics and Gynecology. 4th ed. Philadelphia: Saunders; 2004:108.)

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Anthropoid

Platypelloid Gynecoid Android

Figure 61-2. The four basic pelvic types (Caldwell-Moloy classification). The dotted line indicates the transverse diameter of the inlet. (From Hobel CJ, Chang AB. Normal labor, delivery, and postpartum care. In: Hacker NF, Moore JG, Gambone JC, eds. Essentials of Obstetrics and Gynecology. 4th ed. Philadelphia: Saunders; 2004:109.)

• Internal monitoring: performed by threading a pressure catheter through the cervix, around the presenting part of the fetus, and into the uterine cavity. This method provides information on both the strength and frequency of contractions. 10. What is a normal contraction pattern? A normal contraction pattern during labor consists of three to five contractions in 10 minutes, aver- aged over a 30-minute period. 11. What is an “adequate” contraction pattern? An adequate contraction pattern refers to contractions of sufficient frequency and strength to cause cervical change. Uterine contractions can be measured in Montevideo units. To calculate Montevideo units, total vertical displacement above resting uterine tone is multiplied by contraction frequency over a 10-minute period (Fig. 61-3). An intrauterine pressure catheter must be used. Contractions are considered adequate when they reach 200 Montevideo units or greater.

100 100 12 12 75 10 75 10 8 8 50 50 6 6 4 25 25 2 2 UA 0 mm Hg 0 kPa UA 0 mm Hg 0 kPa Figure 61-3. Calculation of Montevideo units. UA, Uterine activity. (From Bashore RA, Koos BJ. Fetal surveillance during labor. In: Hacker NF, Gambone JG, Hobel CJ, eds. Hacker and Moore’s Essentials of Obstetrics and Gynecology. 5th ed. Philadelphia: Saunders; 2010.)

12. What are the two phases of the first stage of labor? The first stage is divided into a latent phase and an active phase. The duration of the latent phase is variable and has little bearing on the subsequent course of labor, whereas the characteristics of the active phase are usually predictive of the outcome of a particular labor. 13. What is the Friedman curve? In the 1950s, Emanuel A. Friedman popularized the use of an objective measure of labor progres- sion. He constructed a graphic representation of expected cervical dilation against time, with varying expectations for nulliparous and multiparous patients. Used in conjunction with fetal descent, these curves were used to provide clinical feedback about the normalcy of a patient’s labor progress. “Labor curves” have since been updated in light of changing demographics, improved statistical and experimental methods, and more robust study designs. 14. What cervical changes generally take place during the latent phase of labor? Although little cervical dilation occurs during this time, considerable changes take place in the extracellular matrix (collagen and other connective tissue components) of the cervix. Cervical ripening generally includes palpable softening, effacement, and anterior rotation of the cervix in the pelvic axis. 15. When does conversion from the latent to active phase occur? During labor, the transition is characterized by increased regularity and intensity of contractions, accompanied by progressive and predictable cervical change. The active phase of labor begins at 6 cm dilation and accelerates at different rates based on parity. 16. What is the duration of the first stage of labor? • Latent phase: The median duration and 95th percentile duration of the latent phase depend on baseline cervical dilation and are similar between nulliparous and parous women. If a patient is admitted to the hospital at 2 cm dilation, the median duration of the latent phase is approximately 6 hours, and the 95th percentile is 15.7 hours. If a patient is admitted at 3 cm, the median duration is approximately 4 hours, and the 95th percentile is 12.5 hours. The term prolonged latent phase is used to indicate that a patient has been in the latent phase of labor for longer than the 95th percentile. • Active phase: The median duration and 95th percentile duration of the active phase in nulliparous women are 2.1 and 8.6 hours, respectively. In parous women, these times are 1.5 and 7.5 hours. The term prolonged active phase is used to indicate that cervical dilation is occurring at a rate of less than the 5th percentile. 17. What is the management of a prolonged latent phase? Options include maternal sedation (also known as “therapeutic rest”), augmentation with oxytocin, or discharge home if the patient and fetus are stable. 18. What is the management of a prolonged active phase? Treatment is either observation or augmentation with oxytocin. 19. How is arrest of the active phase defined, and how is it managed? Arrest of the active phase is defined as cessation of dilation when an adequate contraction pattern (≥200 Montevideo units in a 10-minute period) has been present for 2 hours. Cesarean section is generally indicated in these cases. 20. At how many centimeters is a cervix considered to be fully dilated? At 10 cm, it is considered fully dilated because this is the approximate diameter of the fetal vertex at term. For preterm infants, however, full dilation may be less than 10 cm; the cervix will not dilate past the maximal point of the presenting part. 21. What are the two possible abnormalities of the second stage of labor? Prolonged descent and arrest of descent. Although prolonged descent has traditionally been defined as descent occurring at less than 1 cm/hour in nulliparas and more than 2 cm/hour in multiparas, it does not usually affect clinical management. Arrest of descent is defined as generally considered to occur when there has been no progress (descent or rotation) for a specified amount of time based on parity and whether regional anesthesia is being used: • 4 hours or longer in nulliparous women with an epidural • 3 hours or longer in nulliparous women without an epidural • 3 hours or longer in multiparous women with an epidural • 2 hours or longer in multiparous women without an epidural

If the patient is a candidate for operative vaginal delivery, this may be an acceptable option as long as fetal macrosomia and cephalopelvic disproportion are not suspected; otherwise, cesarean delivery is indicated. 22. What should be assessed during a vaginal examination? • Cervical dilation • Degree of effacement (thinning of the cervix, usually expressed as a percentage) • Fetal station (presenting part described in centimeters in relation to the maternal ischial spines) • Presenting part (e.g., vertex, breech, shoulder) and orientation 23. What are the cardinal movements of labor? Engagement Descent Flexion Internal rotation External rotation Extension Restitution Expulsion Figure 61-4 illustrates the cardinal movements of labor. 24. What is the Ritgen maneuver? Moderate upward pressure is applied to the fetal chin by the operator’s posterior hand, which is covered with a sterile towel, while the vertex is held against the symphysis (Fig. 61-5). This maneuver allows control of the delivery of the head and favors extension, so that the head is delivered with its smallest diameter passing through the introitus and over the perineum. 25. What is shoulder dystocia and how is it managed? Shoulder dystocia is impaction of the fetal shoulders within the maternal pelvis after delivery of the fetal head, thus preventing further expulsion of the infant. Special maneuvers are required to free the anterior shoulder: • McRobert maneuver (acute flexion of the maternal legs) • Suprapubic pressure • Woods corkscrew maneuver (rotating the posterior shoulder of the fetus 180 degrees in a corkscrew fashion) • Delivery of the posterior shoulder (by sweeping the posterior arm of the fetus across the chest) • Rubin maneuver (displacing the anterior shoulder toward the chest of the fetus within the pelvis) • Deliberate fracture of the clavicles • Zavanelli maneuver (involving flexion of the fetal head, replacement of the fetus within the uterine cavity, and emergency cesarean section delivery) 26. How often does shoulder dystocia occur? Although it has traditionally been associated with fetal macrosomia, up to 50% of cases of shoulder dystocia occur in neonates weighing less than 4000 g. Among infants weighing 4000 to 4499 g, the incidence of shoulder dystocia is 1% to 10% in nondiabetic women and 5% to 23% in diabetic women. These numbers rise to 3% to 23% and 20% to 50%, respectively, for infants weighing more than 4500 g. 27. What are the potential complications of shoulder dystocia? For the fetus, shoulder dystocia may be associated with transient brachial plexus palsies, clavicular fractures, humeral fractures, and neonatal death. For the mother, severe perineal lacerations and postpartum hemorrhage can occur. 28. What is an episiotomy, and why is it performed? An episiotomy is incision of the perineum to enlarge the vaginal opening. It was historically thought to prevent excessive stretching of the perineum, but it has now been abandoned for lack of evidence. Episiotomy has been associated, however, with an increased risk of injury to the rectal sphincter. The two types of episiotomy are median (midline) and mediolateral. A median episiotomy is considered easier to repair and to have a less painful recovery, but it also has a higher rate of extension into the rectum. Mediolateral episiotomies are made at a 45-degree angle to the base of the introitus; they have a lower extension rate and may be considered for large infants, a small perineal body, and in some cases of operative vaginal delivery.

A Before engagement B Engagement, flexion, descent

C Descent, rotation D Complete rotation, early extension

E Complete extension F Restitution

G Anterior shoulder delivery H Posterior shoulder delivery Figure 61-4. The cardinal movements of labor. Although labor is a continuous process, eight discrete cardinal movements of labor occur. A, Before engagement. B, Engagement, flexion, and descent.C, Descent and rotation. D, Complete rotation and early extension. E, Complete extension. F, Restitution. G, Anterior shoulder delivery. H, Posterior shoulder delivery. (From Norwitz ER, Robinson JN, Repke JT. Labor and delivery. In: Gabbe SG, Niebyl JR, Simpson JL, eds. Obstetrics: Normal and Problem Pregnancies. 4th ed. Philadelphia: Churchill Livingstone; 2002:365.)

29. What tissue layers are involved in each of the four types of obstetric laceration? • First-degree: the fourchette, perineal skin, and vaginal mucosa, but not the underlying fascia and muscle • Second-degree: as in first-degree lacerations, with the addition of the fascia and muscles of the perineal body • Third-degree: as in second-degree lacerations, with the addition of the anal sphincter • Fourth-degree: as in third-degree lacerations, with the addition of the rectal mucosa (exposing the lumen of the rectum)

Figure 61-5. Ritgen maneuver. The fingers of the right hand, pressing posterior to the rectum, are used to extend the head while counterpressure is applied to the occiput by the left hand to allow controlled delivery of the fetal head. (From Hobel CJ, Chang AB. Normal labor delivery and postpartum care. In: Hacker NF, Moore JG, Gambone JC, eds. Essentials of Obstetrics and Gynecology. 4th ed. Philadelphia: Saunders; 2004:118.)

30. What are the indications for operative vaginal delivery? The indications for operative vaginal delivery include any condition threatening the mother or fetus during the second stage of labor that is likely to be relieved by delivery. Examples of maternal indications are heart disease, pulmonary injury or compromise, certain neurologic conditions, and maternal exhaustion. An common fetal indication is a nonreassuring fetal heart rate pattern. 31. What are general prerequisites for performing an operative vaginal delivery (ABCs)? • There must be adequate anesthesia. • The maternal bladder should be emptied. • The cervix must be completely dilated. • The fetal head must be engaged. • The fontanels and direction of the occiput must be precisely known. • Membranes must be ruptured (“gush of amniotic fluid”). • The maternal pelvis must be assessed to be adequate (“hips”). • An indication should be present. 32. What is asynclitism? Asynclitism is failure of the vertex to descend with the sagittal suture in the middle plane between the front and back of the pelvis. It is detected clinically on examination when either the anterior or posterior parietal bones precede the sagittal suture. When accompanied by molding, asynclitism can lead to erroneous assessments of the true fetal position. 33. How are the different levels of operative delivery described? • In a high operative delivery, the fetal head is not engaged; this type of operative delivery is no longer performed. • A mid operative delivery is when the fetal station is greater than +2 cm but the head is engaged. • A low operative delivery is when the leading point of the fetal skull is at station +2 cm or greater and not on the pelvic floor. • An outlet operative delivery is when the fetal skull has reached the pelvic floor; scalp should be visible at the introitus without separating the labia, the sagittal suture is in an anteroposterior orientation, and rotation of the fetal head does not exceed 45 degrees (i.e., in right or left occiput anterior or posterior position). 34. What are the two general types of operative delivery? Vacuum-assisted delivery and forceps-assisted delivery.

35. What are following forceps: Simpson, Elliot, Tucker-McLane, Kielland, and Piper? • Simpson: fenestrated blades with divergent handles. The greater cephalic curve of the blade is suited for the molded head and when traction is desired. The Luikart modification employs a pseudofenestrated or semifenestrated blade. • Elliot: fenestrated blades with convergent handles. The lesser cephalic curve is suited for the unmolded head and when traction is desired. • Tucker-McLane: solid blades with convergent handles. The lesser cephalic curve is suited for the unmolded head in situations requiring minimal traction; the Luikart modification employs a pseudofenestrated or semifenestrated blade. • Kielland: minimal pelvic curve. It is ideal for rotation of the vertex from the occiput posterior or transverse position to the occiput anterior position. • Piper: used for delivering the aftercoming head of the breech fetus. The pelvic curve is opposite that of other forceps so that the handles are below the level of the blades Figure 61-6 illustrates the classification of forceps.

1 Classial forceps

Pelvic curvature Cephalic curvature Locking handles

Tucker-McLane Tucker-McLane

Simpson Simpson

Elliot Elliot

2 Rotational forceps Sliding lock Sliding lock No pelvic curvature

Kiellands Kiellands

3 Forceps for delivery of aftercoming head of the breech

Longhandles

Piper

No pelvic curvature Piper

Figure 61-6. Classification of forceps. (From Norwitz ER, Robinson JN, Repke JT. Labor and delivery. In: Gabbe SG. Niebyl JR, Simpson JL, eds, Obstetrics: Normal and Problem Pregnancies. 4th ed. Philadelphia: Churchill Livingstone; 2002:381.)

KEY POINTS: LABOR AND VAGINAL DELIVERY 1. Labor begins when uterine contractions of sufficient frequency, intensity, and duration are attained to bring about effacement and progressive dilation of the cervix. 2. A Bishop score is a quantifiable method to assess the likelihood of a successful induction. If unfavorable, cervical ripening can be done by mechanical (e.g., large Foley catheter) or pharmacologic (e.g., prostaglandins, oxytocin) means. 3. Labor has three stages. The first stage (from the onset of contractions to complete dilation) is divided into latent and active phases. Stage 2 is from complete dilation to delivery of fetus, and stage 3 is from delivery of the fetus to delivery of the placenta. 4. The cardinal movements of labor are engagement, descent, flexion, internal rotation, extension, external rotation, and expulsion. 5. Indications for operative vaginal delivery include any condition threatening the mother or fetus during the second stage of labor that is likely to be relieved by delivery.

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