Induction and Augmentation of Labor

Induction and Augmentation of Labor

Valerie Yates Huwe

Induction and Augmentation

Induction and Augmentation of Labor

Induction of labor is the artificial stimulation of uterine contractions before spontaneous onset of labor for the purpose of accomplishing vaginal birth.1 The goal of labor induction is to achieve vaginal delivery.2

Before 41 0/7 weeks’ induction of labor should generally be performed based on maternal or fetal indications. After 41 0/7 weeks’ induction of labor should be performed to reduce the risk of cesarean and the risk of perinatal morbidity and mortality.3

Augmentation of labor is the stimulation of uterine contraction when spontaneous contractions have failed to result in progressive cervical dilatation or descent of the fetus.4 Since uterine activity is characterized by frequency, intensity, and duration of contractions, it may be desirable to augment these forces in a patient who is in labor but not progressing adequately.

Oxytocin is a hormone, a peptide consisting of nine amino acids that is synthesized by the hypothalamus then transported to the posterior pituitary gland where it is released into the maternal circulation in a pulsatile fashion. Oxytocin is released in response to breast stimulation, cervical stretching, and stimulation of the lower genital tract. Oxytocin released in response to vaginal and cervical stretching results in uterine contractions.5 Oxytocin is the most common pharmacologic agent used for both induction and augmentation of labor in the United States.6 It is also the hormone responsible for the “let down” of milk from alveolar cells in the breast during the postpartum period.

Oxytocin increases free intracellular calcium, which is essential for smooth muscle activity. To exert its effect, oxytocin must bind with the oxytocin receptors. Oxytocin receptors in the uterus increase throughout gestation to reach their maximal levels at term.7 In fact, oxytocin receptors at term are increased 300 times over nonpregnant level. Additionally, the increase of actual receptors is also accompanied by an increase in uterine responsiveness to oxytocin at term.3,8 It is important to note that although oxytocin is an effective induction agent for women with a favorable cervix, it is not effective as a cervical ripening agent.9

The pharmacokinetic half-life of oxytocin is generally accepted to be between 10 and 12 minutes.10,11,12,13 Three to four half-lives of oxytocin are needed to reach steady-state plasma concentrations.11 Uterine response to IV oxytocin administration occurs within 3 to 5 minutes of IV administration, and within 40 minutes a steady-state plasma concentration is achieved.14 This information led Seitchik et al. to recommend at least a 40-minute interval between increases of oxytocin to allow time for the oxytocin to reach a steady state and exert its full effect on the uterus.15 This dosing regime is intended to prevent women from receiving higher doses of oxytocin than are necessary.15 Risks associated with oxytocin are generally dose related and the most common side effect is tachysystole. While oxytocin is the most common medication used for labor induction and augmentation, it is also the drug most commonly associated with preventable adverse events during childbirth.16

Tachysystole is now the preferred term to describe excessive uterine activity. Tachysystole is defined as:

  • More than five contraction in 10 minutes, averaged over 30 minutes

  • Contractions lasting 2 minutes or more

  • Contractions of normal duration occurring within 1 minute of each other

  • Insufficient return of uterine tone between contractions when palpated or >25 mm Hg between contractions when measured with an intrauterine pressure catheter (IUPC).1,4,17,18

NOTE: Other terms like hypertonus and hyperstimulation are not well defined and should be avoided.

Common Techniques for Induction and Augmentation of Labor

Common methods of inducing or augmenting labor include the following:

  • Amniotomy—is the artificial rupture of chorioamniotic membranes by a qualified provider using a plastic hook. It can be an effective method of labor induction in multiparous women with cervical dilation of 3 cm or more causing the uterus to begin contracting. For some women, this may be enough necessary stimulation for labor induction and no other medications are necessary. However, there is insufficient evidence on the safety and efficacy of amniotomy alone for labor induction.1

  • Nipple stimulation is a nonmedical method of inducing labor. Some studies have shown that women with favorable cervices who had nipple stimulation were more likely to go into labor within 72 hours compared to similar women who did not receive nipple stimulation. Since oxytocin is released with nipple stimulation, theoretically tachysystole could result; therefore, uterine activity should be monitored. Nipple stimulation can be accomplished manually by the woman or by application of a warm compress to the breast.

  • Stripping membranes—is the separation of the chorioamniotic membrane from the wall of the cervix and the lower uterine segment. This procedure is typically performed in an office visit at ≥39 weeks of gestation by inserting the examiner’s finger beyond the internal cervical os and then rotating the finger 360 degrees along the lower uterine segment. This action causes a release of prostaglandins and may also stimulate oxytocin release.19 Risks include discomfort during the procedure, prelabor rupture of membranes, vaginal bleeding, and irregular contractions.9 Routine membrane stripping is not recommended, given there is no evidence of improved maternal and neonatal outcome.20

  • Use of oxytocin infusion—Intravenous administration of oxytocin stimulates the smooth muscle of the myometrium of the uterus to contract. Oxytocin administration is covered in detail in Skill Unit 1.

Medical Indications for Induction/Augmentation of Labor

Indications for induction of labor are not absolute and should take into consideration maternal and fetal conditions, gestational age, cervical status, and other factors.1 The following are examples of maternal and fetal conditions that may be indications for induction of labor:

  • Abruptio placentae

  • Chorioamnionitis

  • Fetal demise

  • Gestational hypertension

  • Preeclampsia, eclampsia

  • Premature rupture of membranes (PROMs)

  • Postterm pregnancy

  • Maternal medical conditions including but not limited to diabetes mellitus, renal disease, chronic pulmonary disease, chronic hypertension, and antiphospholipid syndrome

  • Fetal compromise—including but not limited to severe fetal growth restriction, isoimmunization, and oligohydramnios

Prerequisites for Induction/Augmentation of Labor

The woman should not have any of the contraindications for induction/augmentation. In addition it is recommended that the following occur1,21:

  • Gestational age, cervical status, pelvic adequacy, fetal size, and fetal presentation should be assessed before the administration of any cervical ripening agents or oxytocin.

  • Because of the known risks, the medical record should document that a discussion was held between the pregnant woman and her healthcare provider about the indications, the agents, and the methods of labor induction and cervical ripening, including the risks, benefits to the mother and the fetus, alternative approaches, and the possible need for repeat induction (if first attempt fails) or cesarean delivery.1,9,23

  • Nulliparous women undergoing induction of labor with unfavorable cervices should be counseled about a two-fold increased risk of cesarean delivery.1,22,23,24

  • A physician capable of performing a cesarean delivery should be readily available.1

(See Fig. 8.1)

FIGURE 8.1 Induction of Labor Checklist. (Adapted from Patient Safety Checklist from ACOG No 5: Scheduling Induction of Labor.)

No, although induction and augmentation have become a safer procedure for both women and their fetuses, there are some women for whom induction and augmentation carry an unacceptable risk.

Contraindications for Induction/Augmentation of Labor

Listed in Display 8.1 are clinical situations in which induction/augmentation should not be attempted.15 This list is the same as the clinical situations contraindicated for spontaneous labor and vaginal birth.

  • Complete placenta previa when the cervical os is completely covered by the placenta. This can be a life-threatening condition, therefore labor should be avoided and the fetus should be delivered by cesarean birth.

  • Vasa previa when the umbilical arteries and veins cross the cervical os in front of the presenting part. It is a life-threatening condition for the fetus.

  • Transverse fetal lie—fetus is not in the proper position for delivery and cannot be delivered vaginally.

  • Umbilical cord prolapse—when the umbilical cord presents before the presenting part, blood flow to the fetus may be compromised. This is an emergency that requires immediate cesarean delivery.

  • Previous classical cesarean delivery uterine contractions induced or augmented might be too powerful and may rupture the scar.

  • Active genital herpes infection—in the presence of an active genital herpetic lesion, a cesarean birth is recommended to prevent transmission to the fetus.

  • Previous myomectomy entering the endometrial cavity—contraction induced or augmented, might be too powerful and may rupture the scar.

Conditions That Require Special Attention during Induction/Augmentation

There are some situations in which induction/augmentation of labor might present problems. These women require careful administration of a uterine stimulant and close monitoring (Display 8.2).

  • Trial of labor after a previous cesarean birth—spontaneous labor appears to decrease the risk of uterine rupture in women desiring a trial of labor after cesarean (TOLAC). If induction of labor is done in this situation, a thorough discussion of the increased risk of uterine rupture must be documented by the provider in the medical record. Prostaglandin preparations for cervical ripening are contraindicated for these women.27

  • Presenting part not engaged in pelvis—there is space between the presenting part and the bony pelvis. With forceful contractions, the fetal membranes can rupture and increase the risk for umbilical cord prolapse. Also, if the presenting part is not engaged, it might indicate the fetus is too large for the pelvis.

  • Severe maternal hypertension—control of maternal blood pressure should be the priority before induction of labor is initiated.

  • Grand multiparity—in a woman who has had several children (five or more), the uterus is more likely to rupture with the powerful contractions caused by the induction/augmentation of labor.

  • Multiple gestations—caution must be taken to prevent tachysystole of an overly distended uterus.

  • Polyhydramnios—the uterus is overly distended and might not respond well. The possibility of an amniotic fluid embolus may be increased.

  • Abnormal or indeterminate fetal heart rate patterns (not requiring emergent birth)—close monitoring of the fetal heart rate is necessary to rapidly identify any deterioration in fetal status.

  • Maternal heart disease—these women may be induced, but require careful monitoring of maternal hemodynamic status throughout the labor and delivery process. Each clinical condition should be individually assessed. Some induction agents may worsen the patient’s cardiac condition and have adverse effects.

Active management of labor (AML) is an augmentation protocol used in many institutions as a strategy to decrease cesarean births for labor dystocia. The goal is to establish effective contractions and accomplish a vaginal delivery within 12 hours of admission. Although active management is often considered a high-dose oxytocin protocol, it is really a labor management protocol and oxytocin administration is just one component of a whole program of labor.

Cervical Ripening

Cervical ripening is the process of effecting physical softening and distensibility of the cervix leading to effacement and dilatation in preparation for labor and delivery.6 A variety of different methods may be used to induce cervical ripening. These include mechanical devices and several different prostaglandin preparations. Before beginning any cervical ripening or induction, assessment of the cervix should be done and a Bishop score assigned. Since cervical status is the most important factor predicting the success of an induction, this score helps to identify those women who would benefit from cervical ripening before beginning an induction of labor.

A Bishop score is a method of evaluating how ready or “ripe” the cervix is for induction.30 A cervical examination is done to evaluate dilatation, effacement, consistency (i.e., softness or firmness), and cervical position, as well as station of the presenting part. The findings are scored on a scale that was developed based on studies of many women undergoing labor induction (Table 8.1). Inductions are more likely to be successful when a woman’s cervix has undergone certain biochemical changes. Based on the assessment findings and using a scoring system for these changes, it identifies which women are good candidates for labor induction.

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Jul 10, 2020 | Posted by in NURSING | Comments Off on Induction and Augmentation of Labor

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