Induction of Labor

Anatomy and Physiology

The uterus includes both the body and the cervix, with the body composed of smooth muscle and the cervix predominantly collagen. The cervix undergoes dynamic changes during pregnancy and labor, such as shortening, thinning, and dilating. Mechanical and pharmacological methods of labor induction can be used to induce these physiological cervical changes. 

Indications

Indications for late preterm, early term, late-term, and post-term delivery timing depend on a patient's obstetrical and medical history. IOL is indicated when it is thought that the outcomes for the fetus, the mother, or both are better than with expectant management, that is, waiting for the spontaneous onset of labor.[3] The American College of Obstetricians and Gynecologists (ACOG) has an extensive list of recommendations on delivery timing, with some of the more common clinical scenarios listed below [4].

• Oligohydramnios with the timing at 36 0/7 to 37 6/7 weeks of gestation
• Fetal intrauterine growth restriction, with no abnormal Doppler, with the timing at 38 0/7 to 39 6/7 weeks of gestation
• Fetal intrauterine growth restriction, with absent end-diastolic flow, with the timing at 34 0/7 weeks of gestation
• Fetal intrauterine growth restriction, with reversed end-diastolic flow, with the timing at 32 0/7 weeks of gestation
• Chronic hypertension, not on medications, with the timing at 38 0/7 to 39 6/7 weeks of gestation
• Gestational hypertension with the timing at 37 0/7 weeks of gestation or at the time of diagnosis if diagnosed later
• Preeclampsia without severe features with the timing at 37 0/7 weeks of gestation or at the time of diagnosis if diagnosed later
• Preeclampsia with severe features with the timing at 34 0/7 weeks of gestation or at the time of diagnosis if diagnosed later
• Pregestational diabetes is well-controlled, with the timing at 39 0/7 to 39 6/7 weeks of gestation
• Gestational diabetes, diet, or exercise controlled, with the timing at 39 0/7 to 40 6/7 weeks of gestation
• Preterm prelabor rupture of membranes with the timing at 34 0/7 weeks of gestation or at the time of diagnosis if diagnosed laterLate-term with the timing at 41 0/7 to 41 6/7 weeks of gestation
• Abruptio placentae
• Chorioamnionitis
• Intrauterine fetal demise

Labor may also be induced for logistic reasons, such as the risk of rapid labor, distance from the hospital, or psychosocial indications. In such circumstances, fetal lung maturity should be established. In the absence of appropriate clinical circumstances, a mature fetal lung test result before 39 weeks of gestation is not an indication for delivery.[2]

Contraindications

Contraindications to IOL include but are not limited to the following:

• Vasa previa or placenta previa
• Transverse fetal presentation
• Umbilical cord prolapse
• History of a prior classical cesarean section
• Active herpes infection
• A previous myomectomy breaching the endometrial cavity[2]

Equipment

Two primary methods of IOL are mechanical and pharmacological. Cervical ripening agents are utilized primarily when the Bishop score is unfavorable (less than 8). Mechanical cervical ripening of the cervix can be done using a Foley catheter or double-balloon device (ie, Cook catheter) placed through the endocervical canal.[2] Osmotic dilators, laminaria, and synthetic dilators are also used for cervical ripening and are placed in the cervical os. Pharmacological forms of IOL include synthetic prostaglandins and synthetic oxytocin. Prostaglandins are used for cervical ripening. Misoprostol, prostaglandin E1 (PGE1), and dinoprostone, prostaglandin E2 (PGE2), are used in various doses and routes of administration. Notably, prostaglandins should be used with caution in women with a history of a low transverse cesarean section due to concerns for uterine rupture[2]. Oxytocin is administered intravenously in varying dosing regimens. Amniotomy is often used with mechanical and pharmacological labor induction methods. 

Personnel

An inpatient obstetric care team includes but is not limited to nurses, midwives, residents, obstetricians, anesthesiologists, neonatologists, pediatricians, and lactation services. All team members should work in harmony to create a safe environment for the pregnant woman and her fetus during labor and postpartum. A trained obstetrician capable of performing a cesarean section should be readily available anytime IOL is used if the need arises to proceed to a cesarean section.[5]

Preparation

Using the Bishop scoring system, the cervix is evaluated on dilation characteristics, station, consistency, effacement, and position. This score is performed in the late third trimester and at IOL. A favorable cervix with a score of 8 or more is likely to result in a vaginal delivery. However, if the score is 3 or less at the start of the IOL, then the chance of successful vaginal delivery is low.[2] As a healthcare provider, it is crucial to review this information with pregnant women to help them better understand the process of IOL.

Before starting IOL, all pregnant women should have consented to the process and understand all benefits, maternal and fetal risks, and alternatives to IOL. Some of the risks of IOL are similar to that of spontaneous labor, including the need to perform a cesarean section, an operative vaginal delivery, chorioamnionitis, non-reassuring fetal heart rate tracing, and postpartum hemorrhage. Reviewing indications for cesarean section and operative vaginal delivery should be discussed before offering IOL. One indication for a cesarean section is a failure of IOL, where cervical dilation has not progressed or continued despite the use of medications with or without amniotomy. American College of Obstetricians and Gynecologists (ACOG) recommends administrating oxytocin for 12 to 18 hours after the performance of amniotomy before proceeding with a cesarean section for a failed IOL.[6]

During the consent process and while preparing women for IOL, it is encouraged to review the different methods of inducing labor. As indicated above, mechanical and pharmacological methods can be used as a single agent or in combination. A 2016 published randomized control trial addressed this concept. When evaluating women with a singleton pregnancy in the vertex presentation with a Bishop score of less than 6, those who received a combination of induction methods, such as a mechanical IOL using a Foley catheter combined with misoprostol or a Foley with syntocinion, had a faster median time to delivery compared to those who received only misoprostol or a Foley catheter alone. However, when adjusting for further variables, a Foley with syntocinon was not better than a single induction method.[7] 

Additional studies and Cochrane reviews compare amniotomy to mechanical and pharmacological induction methods alone. It shows that mechanical induction with a balloon is probably as effective as labor induction with vaginal PGE2. However, a balloon seems to have a more favorable safety profile for the baby. More research on this comparison does not seem warranted. A balloon catheter may be slightly less effective than oral misoprostol, but It remains unclear if there is a difference in safety outcomes for the baby. When compared to low-dose vaginal misoprostol, a balloon catheter may be less effective but probably has a better safety profile for the baby. Future research could focus more on safety aspects for the baby and maternal satisfaction.[8]

As noted above, cesarean section rates and indications for performing cesarean section should be reviewed with all pregnant women before consenting to IOL. There is a strong emphasis on cesarean section rates in the United States in the medical literature and social media. The New England Journal of Medicine (NEJM) recently published the ARRIVE trial that compared cesarean section rates and perinatal outcomes in nulliparous women undergoing elective IOL at 39 weeks of gestation to expectant management. Results demonstrated a significantly lower cesarean section rate in the induction group and no statistically lower adverse perinatal outcomes.[9] This study has received much attention in the obstetric literature and may potentially change induction practice patterns in the country. Additional published work has reviewed maternal outcomes, including cesarean section rates, with labor induction. A retrospective study published in 2013 found decreased odds of cesarean section in nulliparous and multiparous women being electively induced between 37 and 40 weeks of gestation.[10] Moreover, it was found that women were not at increased risk of third or fourth-degree lacerations or operative vaginal deliveries, regardless of gestational age.[10] Aside from these 2 articles, extensive literature has been published analyzing cesarean section rates concerning variables such as parity, gestational age, and maternal characteristics.

Women being induced for a specific indication, such as fetal growth restriction, may inquire about neonatal risks of IOL. The same 2013 retrospective study from California further analyzed neonatal outcomes and found no difference in fetal death, neonatal intensive care unit (NICU) admission, or respiratory distress across gestational age or parity.[10] However, other literature has shown a possible difference in neonatal outcomes for fetuses delivered in the early term at 37 weeks gestation compared to 38 or 39 weeks gestation. A 2009 NEJM study reviewed this topic from data at the Eunice Kennedy Shriver National Institute; it was found that there was a higher rate of both respiratory and non-respiratory complications with neonates delivered at 37 weeks of gestation via cesarean section compared to those delivered at 38 and 39 weeks of gestation. 

Technique or Treatment

Mechanical dilation with a Foley catheter, a double-balloon catheter, or laminaria can be done as part of the induction process. A Foley catheter is passed through the external and the internal cervical os. The balloon is then inflated between 30 milliliters (mL) to 80 mL with normal saline, and the balloon exerts pressure on the internal os to help with cervical dilation.[2] A 2012 American Journal of Obstetrics and Gynecology article demonstrated that an 80 mL inflation volume resulted in a faster induction and less need for syntocinon compared to a volume of 30 mL.[11] With the double balloon, there is 1 balloon applying pressure to the internal os, and a second balloon applying pressure to the external os. Both balloons can be filled with different volumes of normal saline. Whether a Foley or a Cook catheter is used, both devices are generally removed once cervical dilation is 3 to 4 centimeters. Osmotic dilators are also available in different sizes and placed into the cervical os. 

For cervical ripening with misoprostol, there is a range of doses and routes of administration, such as orally, vaginally, or sublingually. Doses of misoprostol range from 25 micrograms (mcg) to 50 mcg.[2] Suppose IOL is planned in the setting of intrauterine fetal demise in the second trimester. In that case, ACOG supports higher doses of prostaglandins, such as 400 mcg every 3 hours for a maximum of 5 doses.[12] PGE2 (dinoprostone) is available as a vaginal insert and gel formulation. The gel formulation is available in 0.5 mg, and the insert is 10 mg.[2] Further pharmacological methods include syntocinon, which is administered intravenously in varying dosing regimens.[2] Dosing is often titrated so that contractions are 2 to 3 minutes apart to cause cervical dilation. Hospitals may have policies on the maximum dose of oxytocin used for pregnant women undergoing a trial of labor after cesarean section. Amniotomy with an "amnio hook" can be performed any time the cervix is dilated and is done based on the provider's discretion. Factors that are taken into consideration before amniotomy include but are not limited to the fetal station, fetal head engagement, patient preference, and pain level at the time of amniotomy.

Complications

More and more women are labor-induced, and indications are often not urgent. This means that the safety aspects of induction methods become more important, although this could be at the expense of effectiveness. Mechanical methods could have advantages over pharmacological methods as they are widely available, low in cost, and may have fewer side effects, such as excessive uterine contractions (uterine hyperstimulation). This could be safer for the baby because if contractions are too long or very close together, the baby may not receive sufficient oxygen. Pharmacological induction can cause uterine tachysystole, with more than 5 contractions in 10 minutes. Tachysystole may lead to fetal decelerations or bradycardia; much literature has been published regarding the risks of uterine tachysystole with prostaglandins.[13] Further complications include intrapartum vaginal bleeding, presence of meconium-stained amniotic fluid, umbilical cord prolapse, pain not relieved with regional anesthesia, perineal lacerations, postpartum hemorrhage, chorioamnionitis, and postpartum endometritis.[2]

Clinical Significance

IOL represents an opportunity to intervene in an ongoing pregnancy to influence delivery timing for maternal or fetal benefit. There is rigorous research that has been published and continues to be published on both the maternal and fetal safety of IOL, especially as it relates to cesarean section rates. Ultimately, further top-quality research evidence should focus on neonate and maternal satisfaction safety aspects.[14]

Enhancing Healthcare Team Outcomes

Pregnant women offered or undergoing IOL should be managed by a coordinated interprofessional team involving the obstetric provider, specialty-trained obstetric nurse, midwives, anesthetic staff, and a neonatology team. Ultimately, whenever there is a change in the pregnant woman's or fetal status, a collaborative effort between all healthcare team members must be made to ensure the pregnant woman's and her fetus(s) health. The nurses and midwives play a crucial role during the IOL process. Clear communication among the interprofessional team members is vital for achieving the best standard of care for pregnant women undergoing IOL and their families. Witten patient information leaflets should be given to pregnant women offered IOL. They should be easy to understand, and women can also be referred to online resources to help them make informed decisions about their pregnancies. 

Nursing, Allied Health, and Interprofessional Team Interventions

Depending on the acuity level of the facility, continuous electronic fetal monitoring is often done during labor. Many healthcare systems require regular documentation of the electronic fetal heart rate and tocodynamometer and notations written for resuscitative interventions in the presence of a category 2 or fetal heart rate tracing. Nursing should alert obstetric providers and anesthetic staff about potential concerns and the possibility of proceeding with an operative vaginal delivery or cesarean section, depending on the patient's stage of labor and fetal heart rate tracing. 

Nursing, Allied Health, and Interprofessional Team Monitoring

Most hospitals have policies or protocols regarding labor induction, medication administration, fetal heart rate monitoring, oral intake during IOL, pain control, maternal observations, and obstetric emergencies. As noted above, fetal heart rate should be monitored, along with the contraction pattern and adequacy of contractions if an intrauterine pressure catheter is present. Electronic medical records often have flowsheets and checklists for nurses to record events during admission. Depending on the patient's medical history, such as a hypertensive disorder or diabetes mellitus (gestational or pregestational), the hospital may have protocols for the frequency of blood pressure or blood glucose assessments, respectively. Patients on high-alert medications during induction, such as antihypertensives, magnesium sulfate, or insulin, may need more frequent monitoring, depending on the hospital's specific protocol. Changes noted by the nurse during these assessments warrant notifying the obstetric care provider to see if further intervention is required, such as administering additional antihypertensives or glucose in hypoglycemia. Other monitoring during IOL may include the timing of amniotomy and the color of amniotic fluid, which can be crucial to inform further management.