Disorders of the Latent Phase

Historically, the first stage of labor has been divided into the latent phase and the active phase based on the work by Friedman in the 1950s. The onset of latent labor is considered to be the point at which regular uterine contractions are perceived. Friedman found that the mean duration of latent labor was 6.4 hours for nulliparas and 4.8 for multiparas, and the 95th percentile for maximum length in latent labor was 20 hours for nulliparous women and 14 hours for multiparous women ( Table 13-2 ). The definitions of prolonged latent phase are still based on the data from Friedman, and modern investigators have not focused on the latent phase of labor.

Because the duration of latent labor is highly variable, even in the setting of a prolonged latent phase, expectant management is appropriate because most women will ultimately enter the active phase . Some women can spend days in latent labor; provided no indication exists for delivery, awaiting active labor is appropriate. With few exceptions, women who do not enter the active phase will either stop contracting or they will achieve the active phase following amniotomy, oxytocin administration, or both.

Another option is to administer “therapeutic rest,” especially if contractions are painful or the patient is exhausted, with an analgesic agent such as morphine to abate or alleviate painful contractions and allow the patient to rest comfortably until active labor begins.

Disorders of the Active Phase

Active labor demarcates a rapid change in cervical dilation. Active-phase abnormalities can be divided into either protraction disorders (slower progress than normal) or arrest disorders (complete cessation of progress). Based on Friedman’s work, the active phase begins once cervical dilation progresses at a minimum rate of 1.2 cm/hr for nulliparous women and 1.5 cm/hr for multiparous women. Labor is considered protracted if less than these minimum rates of change are seen. Rates of cervical dilation varied greatly in Friedman’s report and ranged from 1.2 to 6.8 cm/hr.

Active-phase arrest traditionally has been defined as the absence of cervical change for 2 hours or more in the presence of adequate uterine contractions and cervical dilation of at least 4 cm. However, revisions in the definitions of labor progress have been made using data from the CSL. The threshold for the active phase of labor is now cervical dilation of 6 cm. Before this dilation is achieved, standards of active-phase progress should not be applied. Thus neither a protracted active phase nor arrest of dilation should be diagnosed in a nullipara before 6 cm cervical dilation, and the lower limit of normal active-phase dilation is about 0.5 cm/hr rather than the 1.0 or 1.2 cm/hr reported by Friedman and others.

Several studies have evaluated the optimal duration of oxytocin augmentation in labor protraction or arrest of labor. In a study of more than 500 women, Rouse and colleagues found that extending the minimum period of oxytocin augmentation for active-phase labor arrest from 2 to at least 4 hours allowed the majority of women who had not progressed at the 2-hour mark to deliver vaginally without an adverse effect on neonatal outcome. Thus as long as fetal and maternal status are reassuring, the diagnosis of arrest (i.e., no cervical change) in the first stage of labor should be reserved for women at or beyond 6 cm cervical dilation with membrane rupture and one of the following: 4 hours or more of adequate contractions (e.g., more than 200 Montevideo units) or 6 hours or more of inadequate contractions.

The most common cause of a protraction disorder is inadequate uterine activity. External tocodynamometry is used to evaluate the duration of and time interval between contractions but cannot be used to evaluate the strength of uterine contractions. The external monitor is held against the abdominal wall and records a relative measurement of uterine contraction intensity, which reflects the monitor’s movement as the uterine shape changes. More precise measurements of uterine activity must be obtained with an intrauterine pressure catheter (IUPC). After amniotomy, an IUPC can be placed into the uterus to measure the pressure generated during a uterine contraction. An IUPC is frequently used when inadequate uterine activity is suspected owing to a protraction or arrest disorder. It can also be used to titrate oxytocin augmentation of labor to the desired effect, particularly when an external monitor cannot effectively record contractions. The lower limit of contraction pressure required to dilate the cervix has been observed to be 15 mm Hg over baseline. Normal spontaneous contractions often exert pressures up to 60 mm Hg.

Once inadequate uterine activity is diagnosed with an IUPC in the setting of a protraction or arrest disorder, oxytocin is usually administered. Typically, the dose is increased until labor progresses normally with adequate contractions that occur at 2- to 3-minute intervals and last 60 to 90 seconds, with a peak intrauterine pressure of 50 to 60 mm Hg and a resting tone of 10 to 15 mm Hg (i.e., uterine activity equal to 150 to 350 Montevideo units).

Another common cause of protraction disorders is abnormal positioning of the fetal presenting part. Some examples of malpresentation are an extended, rather than flexed, fetal head; brow or face presentation; and occiput posterior (OP) position. When persistent OP position is present, labor is reported to be prolonged an average of 1 hour in multiparous women and 2 hours in nulliparous women. In one series, sonography showed OP position in 35% of women in early active labor, indicating that this may contribute to prolongation of labor in many women. In another investigation, the prevalence of persistent OP position at the time of vaginal delivery regardless of parity was 5.5% (7.2% in nulliparas and 4.0% in multiparas). The OP position was found to be associated with longer first and second stages and a lower rate of vaginal delivery (26% for nulliparas and 57% for multiparas) when compared with the occiput anterior (OA) position (74% for nulliparas and 92.3% for multiparas). Most fetuses in the OP position undergo spontaneous anterior rotation during the course of labor, and expectant management is generally indicated.

Cephalopelvic disproportion (CPD) refers to the size disproportion of the fetus relative to the mother, and it can be the cause of a protraction or arrest disorder. This is a diagnosis of exclusion that is often made when a protracted labor course is observed. Most frequently, malposition of the fetal presenting part is the culprit rather than true CPD. Unfortunately, despite past efforts, there is no way to accurately predict CPD. In a decision analysis, it has been estimated that thousands of unnecessary cesarean deliveries would need to be performed in low-risk pregnancies to prevent one diagnosis of true CPD.

Evaluation of arrest of the first stage of labor includes an assessment of uterine activity with an IUPC; performance of clinical pelvimetry; and evaluation of fetal presentation, position, station, and estimated fetal weight. Amniotomy and oxytocin therapy can be initiated if uterine activity is found to be inadequate. The majority of gravidas respond to this intervention, resume progression of cervical dilation, and achieve vaginal delivery.

Disorders of the Second Stage

The second stage of labor begins once the cervix becomes fully dilated and ends with the delivery of the neonate. Although fetal descent begins before the cervix becomes fully dilated, the majority of fetal descent occurs once full cervical dilation is achieved. At this time, maternal expulsion efforts may begin. Parity, delayed pushing, use of epidural analgesia, maternal BMI, birthweight, OP position, and fetal station at completed dilation all have been shown to affect the length of the second stage of labor.

In an effort to define a normal second stage of labor, multiple investigators have studied the relationship between the duration of the second stage of labor and adverse maternal and neonatal outcomes. In one secondary analysis of a multicenter randomized study of fetal pulse oximetry in which 4126 nulliparous women were examined, none of the following outcomes were related to the duration of the second stage: 5-minute Apgar score of less than 4, umbilical artery pH less than 7, intubation in the delivery room, need for admission to the neonatal intensive care unit (NICU), or neonatal sepsis. Fewer investigators have examined the duration of the second stage of labor and the relationship to neonatal outcomes in multiparous women. In one study of 5158 multiparous women, when second stage exceeded 3 hours, the risk of 5-minute Apgar scores of less than 7, admissions to the NICU, and composite neonatal morbidity were all increased.

With appropriate monitoring, however, the absolute risks for adverse fetal or neonatal consequences of increasing second-stage duration appear to be, at worst, low and incremental. Although the risk of a 5-minute Apgar score below 7 and neonatal depression at birth were statistically increased when the second stage was longer than 2 hours, in a study of 58,113 multiparous women, the absolute risk of these outcomes was low (<1.5%) with a second-stage labor duration less than 2 hours, and it did not double even with durations greater than 5 hours. Given the findings in these studies, the absolute permissible maximum length of time spent in the second stage of labor has not been identified.

Protraction of descent is defined as descent of the presenting part during the second stage of labor that occurs at less than 1 cm/hr in nulliparous women and less than 2 cm/hr in multiparous women. Arrest (failure) of descent refers to no progress in descent. Both diagnoses require evaluation of five factors: (1) uterine activity, (2) maternal expulsive efforts, (3) fetal heart rate status, (4) fetal position, and (5) clinical pelvimetry. Decisions then may be made regarding interventions, such as increasing or initiating oxytocin infusion to improve maternal expulsive efforts or proceeding with operative vaginal or cesarean delivery. Management of the second stage of labor can be difficult, and decisions regarding intervention must be individualized.

The median duration of the second stage is 50 to 60 minutes for nulliparas and 20 to 30 minutes for multiparas, but the range of second-stage duration is highly variable. Janakiraman and colleagues compared the second stage in 3139 induced women to that of 11,588 women in spontaneous labor. No differences in the length of the second stage or in the risk of a prolonged second stage were noted between the groups, although the induced nulliparas appeared to be at increased risk for post­partum hemorrhage and cesarean delivery (4.2% vs. 2.0%, odds radio [OR] 1.62; 95% confidence interval [CI], 1.02 to 2.58; and 10.9% vs. 7.2%, OR 1.32; 95% CI, 1.01 to 1.71, respectively).

In classic obstetric teaching, the upper limit for the duration of the second stage of labor was considered to be 2 hours. In the available literature, before diagnosing arrest of labor in the second stage—and if maternal and fetal conditions permit—it suggests at least 2 hours of pushing should be allowed with multiparous women, and at least 3 hours should be allowed with nulliparous women. Longer durations may be appropriate on an individualized basis (e.g., with epidural analgesia or with fetal malposition) as long as progress is documented. The labor guidelines from the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD) suggest allowing at least 1 additional hour if an epidural is present (i.e., at least 3 hours in multiparous and at least 4 hours in nulliparous women) before diagnosing second-stage arrest. A specific absolute maximum length of time spent in the second stage of labor beyond which all women should undergo operative delivery has not been identified.

Many authors have studied the perinatal and maternal effects of a prolonged second stage. Several studies found no increase in infant morbidity or mortality with a second stage lasting longer than 2 hours, although the rate of vaginal delivery decreased after 3 hours in the second stage. However, a recent population-based cohort study by Allen and colleagues examined 63,404 nulliparous women and found increased risks of low 5-minute Apgar score, birth depression, and admission to the NICU with increasing duration of the second stage greater than 3 hours. This study is the largest thus far to evaluate neonatal and maternal outcomes with a prolonged second stage. In this study, as well as others, evidence shows that maternal morbidities—including perineal trauma, chorioamnionitis, instrumental delivery, and postpartum hemorrhage—increase with prolonged second stages that last greater than 2 hours .

Disorders of the Third Stage

The third stage of labor is the period from delivery of the infant to the expulsion of the placenta. Separation of the placenta is the consequence of continued uterine contractions. Signs of placental separation include a gush of blood, lengthening of the umbilical cord, and change in shape of the uterine fundus from discoid to globular with elevation of the fundal height. The interval between delivery of the infant and delivery of the placenta and fetal membranes is usually less than 10 minutes and is complete within 15 minutes in 95% of deliveries. The most important risk associated with a prolonged third stage is hemorrhage; this risk increases proportionally with increased duration. Because of the associated increased incidence of hemorrhage after 30 minutes, most practitioners diagnose retained placenta after this time interval has elapsed. Interventions to expedite placental delivery are usually undertaken at this point.

Management of the third stage of labor may be expectant or active. Expectant management refers to the delivery of the placenta without cord clamping, cord traction, or the administration of uterotonic agents such as oxytocin. Active management consists of some combination of early cord clamping, controlled cord traction, and administration of a uterotonic agent. Oxytocin is the usual uterotonic agent given, but others have been used, such as misoprostol or other prostaglandin compounds. Compared with expectant management of the third stage, active management has been associated with a reduced risk of postpartum hemorrhage. Cochrane reviewers evaluated five trials that comprised 6486 women and compared active and expectant management. They confirmed that active management reduced the risk of maternal hemorrhage (relative risk [RR], 0.34; 95% CI, 0.14 to 0.87) but that significant increases in maternal diastolic blood pressure, afterpains, and analgesia use occurred as well. These adverse events may reflect the side effects of the various uterotonic medications used in different countries.

Some debate exists regarding the timing of oxytocin administration when active management of the third stage is practiced—that is, whether it should be after the placenta has delivered or after the anterior shoulder of the fetus has delivered. A randomized controlled trial (RCT) that included 1486 women compared the effects of oxytocin administration upon delivery of the anterior shoulder to administration after delivery of the placenta and showed no significant differences in blood loss or retained placenta between the groups.

Retained placenta can usually be treated with measures such as manual removal or sharp curettage. Attempting manual removal can be performed under regional anesthesia or conscious sedation. If this is not successful, a sharp curettage can be performed under sonographic guidance. Prophylactic broad-spectrum antimicrobial agents are often administered when manual removal of the placenta is performed, although little evidence supports or refutes their use.

Anesthesia Effects on Labor Progress

Conduction epidural anesthesia’s effect on the rate of cervical change remains controversial, (see Chapter 16 ). Unfortunately, RCTs have several limitations, mainly that there cannot be a placebo group. Thus multiple randomized trials have investigated cesarean delivery rates between women who received epidural anesthesia versus those who received systemic analgesia in labor. A 2005 Cochrane review that involved 20 studies reported no increase in cesarean delivery rates between women who received epidural anesthesia versus those who received systemic analgesia for labor (RR, 1.07; 95% CI, 0.93 to 1.23). A more recent meta-analysis that involved 15 RCTs and included 4619 patients also compared the effects of epidural anesthesia to parenteral opioids. The incidence of cesarean delivery was the same between the groups, although the incidence of operative vaginal delivery was increased in the conduction anesthesia group [OR, 1.92; 95% CI, 1.52 to 1.22). It has been difficult to establish whether this increase in operative vaginal delivery was due to a direct effect of the epidural analgesia on the progress of labor or an indirect effect, such as greater opportunities for resident training. No difference in the duration of the first stage was noted; however, the second stage was prolonged by approximately 16 minutes (95% CI, 10 to 23 minutes). This statistically significant finding lacks clinical relevance.

It has also been suggested that receiving epidural anesthesia during latent labor, as opposed to during the active phase, results in prolongation of the labor. Accordingly, many practitioners refrain from administering epidural analgesia until the patient reaches 4 cm or more dilation. In one investigation, 12,693 nulliparas were randomized to receive early epidural analgesia (at first request if cervical dilation was at least 1 cm) or late epidural analgesia (parenteral meperidine until cervical dilation of 4 cm was achieved). The median cervical dilation at the time of epidural placement was 1.6 cm for the early group and 5.1 for the late group. These researchers found no difference in the incidence of cesarean birth, operative vaginal delivery, or length of the first or second stages of labor.

Pharmacologic Augmentation

When the first stage of labor is protracted or an arrest disorder is diagnosed, an evaluation of uterine activity; clinical pelvimetry; and fetal position, station, and estimated weight should be performed. If uterine activity is found to be suboptimal, the most common remedy is oxytocin augmentation. Various oxytocin dosing regimens have been described in the obstetric literature. Local protocols for oxytocin administration should include the dose of oxytocin being delivered (mU/min) as opposed to the volume of fluid being infused (mL/min) and should specify initial dose, incremental increases with time, and maximum permissible dose. Although oxytocin currently is used in a majority of labors in the United States, it is important for clinicians to recognize that it is also the medication implicated in approximately half of all paid obstetric litigation claims, and it is the medication most commonly associated with preventable adverse events during childbirth.

Misoprostol solution given orally has been proposed as an alternative augmentation agent. Ho and colleagues randomized 231 women to a solution of 20 µg misoprostol, prepared by dissolving one 200-µg tablet of misoprostol in 200 mL tap water, or to intravenous (IV) oxytocin. The results of this admittedly small study revealed similar rates of vaginal delivery between the two groups, and no difference was noted in side effects or neonatal outcomes.

Side Effects

One of the advantages of oxytocin administration is that if uterine overactivity is encountered, the infusion can quickly be stopped, and the half-life of oxytocin is approximately 3 minutes. The most frequently encountered complication of oxytocin or prostaglandin administration is uterine overactivity. However, until an NICHD workshop attempted to provide standardized nomenclature for uterine activity and electronic fetal heart monitoring, no uniform definitions existed for terms like hyperstimulation and tachysystole . These guidelines define tachysystole as more than five contractions in 10 minutes averaged over a 30-minute window, and they recommend abandoning the terms hyperstimulation and hypercontractility .

Because oxytocin is structurally and functionally related to vasopressin, one of its side effects is, in rare instances, water intoxication and hyponatremia. Historically, bolus injections of oxytocin were thought to cause hypotension, and the current practice for labor management is administration by infusion pump or slow drip. Some investigators have suggested that a 10-IU bolus of oxytocin given in the third stage of labor is not associated with adverse hemodynamic responses compared with oxytocin given as an infusion. However, Jonsson and colleagues found that an IV bolus was associated with ST depressions seen on the electrocardiogram. Given that no advantage has been found with the use of IV boluses of oxytocin, and given the potential hemodynamic adverse consequences, this form of administration is not recommended. Finally, uterine rupture is rare and in most instances occurs in women who have had a prior uterine surgery, such as a cesarean delivery or myomectomy.

Recent investigations have shed light on the question of labor augmentation and induction for women attempting a trial of labor after cesarean delivery (TOLAC; see Chapter 20 ). Whereas no randomized trials have been done, a large prospective investigation evaluated more than 17,000 women attempting TOLAC. The incidence of uterine rupture was 0.4% for those subjects who spontaneously labored versus 0.9% for those who received augmentation and 1.0% for subjects who underwent induction. Other complications of attempting TOLAC are illustrated in Table 13-3 . ACOG currently recommends the use of oxytocin in augmentation and induction of women undergoing a TOLAC.

Indications and Contraindications

Induction of labor should be undertaken when the benefits of delivery to either mother or fetus outweigh the risks of pregnancy continuation. Many accepted medical and obstetric indications for labor induction exist ( Table 13-4 ). Contraindications include those that preclude vaginal delivery ( Table 13-5 ).

With regard to induction of labor versus expectant management for gestational hypertension or preeclampsia without severe features, investigators in the Netherlands performed a trial in which 756 patients were randomized to receive induction ( n = 377) or expectant monitoring ( n = 379). Of women who were randomized to induction of labor, 117 (31%) experienced poor maternal outcome compared with the 166 (44%) allocated to expectant management (RR, 0.71; 95% CI, 0.59 to 0.86; P = .0001). No cases of maternal or neonatal death or eclampsia were recorded. Thus in women with gestational hypertension or preeclampsia without severe features, induction of labor is associated with improved maternal outcome, and it should be advised at 37 weeks’ gestation.

“Impending” macrosomia, a favorable cervix, patients considered to be at increased risk for preeclampsia (such as having a prior history of preeclampsia), or concerns about intrauterine growth restriction (e.g., a fetus with an estimated weight at the 19th percentile) are not accepted medical indications for induction. Additionally, preterm or early-term induction is not medically indicated for maternal anxiety or discomfort related to normal pregnancy, previous pregnancy with labor abnor­malities such as rapid labor or shoulder dystocia, or simply because the mother lives far from the hospital. Currently, experts concur that elective induction should not be performed before 39 weeks of gestation; however, insufficient data are available to recommend for or against induction of labor at 39 or more weeks of gestation.

Examination of the maternal and fetal condition is required before undertaking labor induction ( Table 13-6 ). Indications and contraindications for induction should be reviewed along with the alternatives. Risks and benefits of labor induction should be discussed with the patient, including the risks of cesarean delivery (discussed later). Confirmation of gestational age is critical, and evaluation of fetal lung maturity status should be performed if indicated ( Table 13-7 ). Fetal weight should be estimated, clinical pelvimetry should be performed, and fetal presentation should be confirmed; in addition, a cervical examination should be performed and documented, and labor induction should be performed at a location where personnel are available who are familiar with the process and its potential complications. Uterine activity and electronic fetal monitoring (EFM) are recommended for any gravida receiving uterotonic medications.

Prolonged Pregnancy

In a joint Committee Opinion, the ACOG and SMFM discourage the use of the label term pregnancy and instead have replaced it with the labels early term, full term, late term, and postterm . Postterm pregnancy (≥42 weeks of gestation) is associated with increased risks for the fetus and mother (see Chapter 36 ). According to a large epidemiologic study by Hilder and colleagues, the perinatal mortality rate—which combines stillbirths (fetal death after 20 weeks’ gestation) and early neonatal deaths (death of a liveborn infant within the first 28 days of life)—at greater than 42 weeks of gestation is approximately twice that at term (4 to 7 deaths vs. 2 to 3 deaths per 1000 deliveries) and increases more than sixfold at 43 weeks of gestation and beyond.

Two more recent studies consisted of prospective cohort evaluations of singleton pregnancies based on ultrasound dating. Nakling and Backe found the incidence of postterm pregnancies to be 7.6% in the cohort, with 0.3% of pregnancies progressing to 301 days (43 weeks’ gestation) if inductions were not permitted prior to 43 weeks. This investigation found a significantly increased rate of perinatal mortality after 41 weeks’ gestation. In contrast, Heimstad and colleagues found an increased trend toward intrauterine fetal demise at 42 weeks’ gestation compared with that at 38 weeks, but this study allowed inductions prior to 43 weeks and did not calculate the perinatal mortality rates. Factors that may contribute to the increased rate of perinatal deaths are uteroplacental insufficiency, meconium aspiration, intrauterine growth restriction (IUGR), and intrauterine infection. For these reasons, common practice has been to deliver patients by 42 0/7 weeks.

Postterm pregnancy is also associated with increased risks for the pregnant woman, including an increase in labor dystocia (9% to 12% vs. 2% to 7% at term) and an increase in severe perineal injury (3.3% vs. 2.6% at term).

Overall, comparisons of induction of labor to expectant management in observational studies have found no difference in, or a decreased risk of, cesarean delivery among women who are induced. This is also true for women with an unfavorable cervix. For example, a meta-analysis revealed that women at less than 42 0/7 weeks’ gestation who underwent induction of labor had a lower cesarean section delivery rate than those who received expectant management. In this meta-analysis, 11 RCTs and 25 observational studies were included and overall, expectant management of pregnancy was associated with a higher odds of cesarean delivery than was induction of labor (OR, 1.22; 95% CI, 1.07 to 1.39). Also, in a 2012 Cochrane meta-analysis of three smaller studies of induction of labor at 41 0/7 weeks, a reduction in the rate of cesarean delivery was demonstrated. Thus the evidence base suggests that labor inductions at 41 0/7 weeks should be performed to reduce the risk of cesarean delivery and the risk of perinatal morbidity and mortality.

Elective Induction of Labor

The rate of induction of labor more than doubled from 1990 through 2010, from 9.6% to 23.8%. Induction rates were at least twice as high in 2010 compared with 1990 for women at all gestational ages except for those in the post term, whose rate of induction rose 90%. Reasons for the general increase over time in inductions include the availability of better cervical ripening agents, patient and provider desire for a more convenient time of delivery, and more acceptance of a variety of indications for induction. Nevertheless, the overall induction rate declined slightly in 2011, to 23.7% (from 23.8% in 2010), and then it declined again in 2012, to 23.3%. Induction rates were lower for all gestational age categories.

Elective induction of labor refers to the initiation of labor for convenience in an individual with a term pregnancy who is free of medical or obstetric indications. Although elective induction at or after 39 weeks of gestation is not recommended or encouraged, it may be appropriate in specific instances, such as for women with a history of very short labors or those who live a great distance from the hospital. Also, a patient who has experienced a prior stillbirth at or near term may request labor induction to ease anxiety and fears about the loss of a subsequent pregnancy. In addition, certain maternal medical conditions require multispecialty participation, in which the benefit of a planned delivery in order to have experienced personnel readily available is most appropriate, such as when a fetal anomaly is present.

Some concerns have been raised that induction of labor increases the rate of cesarean delivery and increases health care costs. Seyb and colleagues noted in their investigation that the mean time spent on labor and delivery was almost twice as long, and postpartum stays were prolonged for those induced. The total cost associated with hospitalization for elective induction was also 17.4% higher than for those in spontaneous labor. These findings were confirmed in investigations by Maslow and Sweeney and Cammu and colleagues.

However, these results are based on the faulty comparison of women who are induced with those in spontaneous labor. In fact, most observational studies that compare induction of labor to expectant management—which is the actual clinical alternative to labor induction—have found either no difference or a decreased risk of cesarean delivery among women who are induced. Because these studies are retrospective in nature, they should be interpreted with caution.

In addition, several RCTs have been recently undertaken. In a meta-analysis by Caughey and colleagues, nine RCTs were evaluated. These trials utilized patients undergoing expectant management, rather than spontaneous labor, as the comparison group for the patients being electively induced, and the meta-analysis revealed a decreased risk of cesarean delivery in the induction group compared with the group managed expectantly (RR, 1.17; 95% CI, 1.05 to 1.29). Similarly, Cochrane reviewers examined 19 trials that included 7984 women and found that women induced at 37 to 40 completed weeks were less likely to have a cesarean delivery than those in the expectant management group (RR, 0.58; 95% CI, 0.34 to 0.99). Caughey and colleagues also examined the risk of cesarean delivery for each week of gestational age ranging from 38 to 41 weeks. In their retrospective study, which again compared induction to expectant management, cesarean delivery was decreased in the induction groups.

With regard to perinatal outcomes, it appears that compared with infants who undergo spontaneous labor, fewer electively induced infants have meconium passage and therefore likely have a reduced incidence of meconium aspiration syndrome. Macrosomia also may be reduced, as noted in an ecological study performed by Zhang and colleagues. This study revealed that the increased induction rate between 1992 and 2003 (14% to 27%) was significantly associated with reduced mean fetal birth weight ( r = −0.54; 95% CI, −0.71 to −0.29) and rate of macrosomia ( r = −0.55; 95% CI, −0.74 to −0.32).

The risk of respiratory morbidity associated with labor induction was illustrated in a retrospective review of infants admitted to the NICU following elective delivery at term. These results support delaying elective delivery until 39 weeks’ gestation ( Table 13-8 ). In further support of these findings, Clark and colleagues performed a prospective observational study of 27 hospitals that included 17,794 deliveries. Of these, 14,955 (84%) occurred at 37 weeks or greater; 6562 (44%) of them were planned deliveries, rather than spontaneous. Among the planned deliveries, 4645 (71%) were elective. The percentage of the electively delivered infants admitted to the NICU was 17.8% ( n = 43) at 37 to 38 weeks, 8% ( n = 118) at 38 to 39 weeks, and 4.6% ( n = 135) at 39 weeks. These studies reiterate the importance of considering neonatal morbidity with elective induction prior to 39 weeks’ gestation. After 39 weeks, however, one study has suggested that infants of electively induced mothers were less likely to receive ventilatory support, become septic, or be admitted to the NICU.

TABLE 13-8

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1. Antepartum Fetal Evaluation
2. Cesarean Delivery
3. Prolonged and Postterm Pregnancy
4. Mental Health and Behavioral Disorders in Pregnancy

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