Induction of Labor

CHAPTER 163 Induction of Labor



Scott T. Henderson


Although labor usually begins spontaneously, the induction of labor is one of the most common procedures in obstetrics. It is indicated for both maternal and fetal reasons as well as for elective and social reasons. The frequency at which patients undergo induction of labor has risen from 9% in 1989 to over 20% today. To induce labor, it may also be necessary to manipulate the cervical connective tissue. Therefore, induction can be viewed in two phases, cervical ripening followed by induction of contractions by artificial stimulation of the uterus.


The status of the cervix plays a vital role in the success or failure of an induction. The Bishop Scoring System is a tool that has been used for many years to help quantify the readiness of the cervix for labor (Table 163-1). The maximum score is 13. When the score exceeds 8, the likelihood of a successful vaginal delivery with use of oxytocin approaches that of spontaneous labor. A Bishop score of less than 6 correlates with a prolonged labor or failed induction. For research purposes, there is slight variation in the definition of an unfavorable cervix, with a Bishop score ranging from 4 to 6.



TABLE 163-1 Bishop Scoring System

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When a cervix is assessed as not favorable, ripening methods should be considered. Historically, nonpharmacologic methods such as breast stimulation, acupuncture, stripping (sweeping) of membranes, and placement of a Foley catheter or laminaria in the cervical os have been used. With the development of artificial prostaglandins (dinoprostone [prostaglandin E2; PGE2] and misoprostol [PGE1]), use of pharmacologic methods has surpassed these other methods. If a cervix is favorable or ripening techniques have been used, it is reasonable to use oxytocin or amniotomy (see Chapter 164, Amniotomy) to stimulate the uterus to have regular and rhythmic contractions.


Providers and nursing staff should develop protocols, as a team, for management of labor induction, including possible complications. These policies should be in written form and followed to maximize safety for the mother and infant and to reduce liability for the providers and institution. Protocols should outline not only the procedural technique but the indications and contraindications. Special attention should be given to the protocols for elective inductions and for induction in women with a previous cesarean section.



Anatomy


The uterus is normally spontaneously contractile. During gestation, various physiologic mechanisms maintain it in an inactive state. Retention of the fetus is also aided by the cervix, a tight sphincter composed mainly of connective tissue, which maintains the pregnancy’s integrity. During the final 4 to 5 weeks of pregnancy, the cervix normally undergoes a “ripening” process. Hormone-mediated changes alter the cervix in both composition and structural organization. It becomes softer and more pliable, and dilates. Endogenous prostaglandins play an important role in this process and also sensitize the uterus to prepare for labor.



Indications


Induction is indicated when the benefits of delivery to the mother or fetus outweigh the potential risks of continuing the pregnancy. Pregnancy-induced hypertension and prolonged or post-term pregnancies are among the most common indications, accounting for more than 80% of reported inductions. Indications include the following:


• Pregnancy-induced hypertension, preeclampsia, or eclampsia

• Prolonged or post-term pregnancy

• Abruptio placentae

• Abnormal antepartum testing results and delivery indicated

• Chorioamnionitis

• Suspected fetal compromise (e.g., severe fetal growth restriction, isoimmunization)

• Fetal demise

• Premature rupture of membranes

• Maternal medical complications (e.g., diabetes mellitus, renal disease, chronic pulmonary disease, chronic hypertension)

Elective (without medical or obstetric indications) induction of labor is generally not recommended. However, logistic factors such as distance from the hospital, a history of rapid labor and delivery, or psychosocial issues may be reasonable indications for elective induction.



Contraindications



Absolute


Absolute contradictions are the same as those for spontaneous labor or delivery, including the following:


• Placenta previa

• Vasa previa

• Transverse fetal lie

• Severe hydrocephalus

• Prolapsed umbilical cord

• Previous classic cesarean incision or other longitudinal uterine scar

• Small maternal size or distorted pelvic anatomy

• Active genital herpes infection

• Invasive cervical carcinoma

• Nonreassuring fetal status

• Known hypersensitivity to prostaglandins (dinoprostone [PGE2] or misoprostol [PGE1])

• Previous asthma, glaucoma, or myocardial infarction (dinoprostone)


Relative



• Multiple gestation

• Polyhydramnios

• Appreciable macrosomia

• Maternal cardiac disease

• Grand multiparity

• Previous cesarean delivery

• Breech presentation

• Malpresentations

• Presenting part above pelvic inlet

• Unexplained vaginal bleeding during pregnancy

• Prematurity

• Ruptured membranes


Equipment and Supplies



• External device for monitoring fetal heart rate (FHR) and uterine activity.

• Sterile gloves.

• Sterile speculum (if membranes ruptured or using dinoprostone gel).

• Intravenous (IV) access (e.g., heparin lock, lactated Ringer’s, normal saline).

• Pharmacologic induction supplies: dinoprostone (PGE2) gel 0.5 mg in 2.5 mL (Prepidil) or insert 10 mg (Cervidil); misoprostol (PGE1) 100-µg tablet; or oxytocin 10 U/mL (Pitocin).

NOTE: Dinoprostone should be stored between −20° C and −10° C. Because misoprostol is available only in a 100-µg dosage, it is recommended to have the pharmacist cut the tablet into quarters to ensure the correct dose.


EDITOR’S NOTE: A meta-analysis of randomized, controlled trials comparing dinoprostone with misoprostol for cervical ripening and induction of labor found the time to delivery was shorter and the rate of cesarean delivery was lower in the misoprostol group.



• Oxytocin, usually 10,000 to 20,000 mU is diluted in 1 L of lactated Ringer’s or normal saline to provide a 10 to 20 mU/mL mixture.

• Infusion pump, if oxytocin is to be used.

• Mechanical induction device (16- to 26-Fr Foley catheter or laminaria [from the brown, cold-water seaweed Laminaria digitata or japonica], available in small, medium, and large sizes) and povidone–iodine solution, sterile 4 × 4 gauze sponges, sponge or uterine packing forceps. One author (Freedman, 2002) suggests use of a blunt-tipped stylet (urologic sound) to help with insertion of the Foley.

• Terbutaline 0.25 mg (at least two doses should be readily available before initiating use of dinoprostone or misoprostol).


Precautions


Before proceeding with an elective induction, the provider should review and confirm the dating of pregnancy by at least one of the following:


1 Fetal heart tones present for 30 weeks by fetal Doppler or 20 weeks by nonelectronic fetoscope

2 Thirty-six weeks since a positive β-human chorionic gonadotropin

3 A crown–rump length obtained at 6 to 12 weeks that supports a gestational age of at least 39 weeks

4 An ultrasonographic study obtained at 13 to 20 weeks that confirms the gestational age of at least 39 weeks

5 Documented fetal lung maturity by amniocentesis (see Chapter 161, Amniocentesis)

Before proceeding with induction in a patient who has had a previous caesarean section, the provider must consider the fact that these patients have an increased rate of uterine rupture, especially those with a failed trial of labor. Although labor induction may be a reasonable option for patients attempting vaginal birth after a cesarean delivery (VBAC), the risk of uterine rupture should be discussed with the patient and documented in the medical record.


EDITOR’S NOTE: At many institutions, documented informed consent is required before induction of labor or VBAC.


Caution should be exercised with the use of dinoprostone in patients with ruptured membranes and in patients with a history of previous uterine hypertonia, glaucoma, myocardial infarction, or childhood asthma (even if there have been no asthma attacks in adulthood).



Preprocedure Patient Education and Forms


All patients should be counseled regarding the indications for induction, the expected results, the alternatives, and the possible adverse effects, including the increased risks for cesarean section, uterine hyperstimulation, and fetal distress. The U.S. Food and Drug Administration (FDA) has approved only oxytocin and dinoprostone for labor induction. Review the possible complications with the patient (and family, if present). The clinician should be familiar with the package insert information. With use of prostaglandins, vomiting, diarrhea, or fever may occur, but a recent review of the literature indicated no difference between treatment and control for use of prostaglandins for cervical ripening. Laminaria are made from brown seaweed and act by drawing water from the cervix and swelling, which softens and then dilates the cervix. If a laminaria is inserted, some clinicians will let the patient go home; however, there is a slight increased risk of infection. Anaphylaxis has also been reported. With either laminaria or Foley catheter, the patient will typically experience cramping as the cervix dilates.


Misoprostol is not approved by the FDA for this use. There is a “black box warning” against the use of misoprostol during pregnancy. Patients should be informed of the off-label use and possible complications of any prostaglandin, as listed later. It may be helpful to remind the patient that clinicians frequently use medications off-label (e.g., most of the common medications used to halt preterm labor are off-label). Furthermore, misoprostol is contraindicated in patients who have had a previous cesarean delivery.

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May 14, 2017 | Posted by in GENERAL & FAMILY MEDICINE | Comments Off on Induction of Labor

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