This article reviews of methodologies for the induction of uterine contractions so that labor may occur. Physicians induce labor to promote vaginal delivery and to prevent complications of obstetric intervention. These complications are diverse and lead to cesarean section. Labor induction rates levels rose from 9.5% in 1992 to as high as 23.8% in 2010. The rates have been fairly stable since then.
The uterus is made up of the corpus (the body of the uterus) and the cervix (the neck of the uterus). The fundus of the uterus is muscular, and the uterine cervix is predominantly collagen tissue. The cervix of the uterus undergoes physical changes in the course of pregnancy. The change is referred to as the ripening of the cervix. The process is exaggerated in the late third trimester. Anatomically, as pregnancy progresses, the cervix softens and is amenable to being effaced secondary to uterine contractions that may be perceived (Braxton Hicks). The endocervical length is essentially ablated in the process and concludes with the initiation of cervical dilation. In summary, the pre-labor process is referred to as cervical ripening, and it precedes the onset of labor. Induction of labor requires artificial acceleration of this pre-labor process. The goal of labor induction is to nudge the parturient into establishing labor.
Indications for induction of labor may be obstetric and medical before 39 weeks of concluded gestation, or it may be elective at 39 weeks or more of gestation. Prior to 37 weeks compelling obstetric and medical indications must be present to justify the risks of prematurity. At 37 weeks, the gestation is assessed to have reached early term, and thus, also requires a specific indication to abbreviated pregnancy before the full term which is 39 weeks. The fetus does not benefit from pregnancy beyond 39 weeks. However, induction of labor entails risk, and thus elective interventions before 41 weeks will require consideration for minimizing risks of failed induction and degenerative complications. Some of the common indications for induction of labor include:
Pleural pregnancies are becoming increasingly common, and the timing of labor depends on the chronicity of the twin gestation. Dichorionic diamniotic twin gestations definitively conclude between 38 and 39 weeks of gestation and induction of labor is definitively permissible with the cephalic presentation of both.
Whenever the risks of cesarean section are considered to be higher than the risks of induction, the obstetric scenario represents a contraindication for induction of labor. Thus a prior classical cesarean section or a history of the corpus of the uterus being disrupted represents a contraindication because of the increased risk of uterine rupture during labor. Prior uterine rupture also represents a contraindication as does placenta previa or vasa previa. Contraindications include a funic presentation (cord prolapse may be anticipated) and malpresentation like a transverse lie. Breech presentations are preferably delivered by cesarean section. Concern for fetal well-being and anticipated intolerance of labor by the fetus are also deterrents to the consideration labor induction.
Induction of labor may involve mechanical ripening of the cervix by placing of a Foley catheter bulb into the endocervical canal, such that it is inflated above the internal cervical opening at the cephaloid end of the endocervical canal. This may be initiated on an outpatient basis in the office; however, the remaining induction methodologies require inpatient care in a labor and delivery suite. The ancillary supportive management requires equipment for fetal monitoring as well medical supplies for establishing intravenous access. Capacity for urgent or emergent cesarean delivery should be available if it is needed. Protocols and applicable equipment for administration of oxytocin and cervical-ripening agents such as prostaglandins (PGE2 gel or PGY1 tablets) should be available.
The personnel falls in the category of nursing support and obstetric attendance that could be diverse ranging from midwives to obstetricians. The nursing personnel should have protocols established to guide obstetric surveillance as well as patient assignment load to allow them to accomplish the clinical tasks. The obstetric staff should be available for oversight of the induction and readiness for cesarean delivery should it become necessary emergently. This is standard practice and an expression of routine foresight in the practice of medicine.
Patient preparation includes obtaining informed consent and patient understanding of the indication for labor induction and the benefits it brings along with the risks of failed induction and iatrogenic complications, both of which may lead to cesarean delivery. Discussion on any available alternatives should be included. Availability of antenatal records and pertinent obstetric laboratory results should be arranged. When the cervical assessment is consistent with an unfavorable cervix, the patient should be apprised of the possibility or requiring serial induction of labor. The Bishop Score assessment described under technique should be reviewed with the patient to foster an understanding of expectations of the procedure.
Bishop Score to assess cervical suitability for induction of labor. A Bishop score of more than 8 suggests that induction is likely to yield a vaginal delivery. The cervix is thus considered favorable for induction, and pre-induction cervical ripening is not necessary. However, if the cervical assessment Bishop Score is 3 or less, then the chances of successful vaginal delivery at the conclusion of the induction is low. Induction of labor should be pursued thoughtfully. A Bishop score between 3 and 6 represents the intermediate risk category for a failed induction.
Update above assessments. Place a Foley bulb into the endocervical canal such that the inflated balloon lies above the internal os. This is an acquired skill but does not require any instrumentation other than the availability of the Foley bulb. Administration of Pitocin intravenously with established protocols, and finally, the administer prostaglandins vaginally either as gel preparations or as tablets.
The determination of success for induction of labor is a successful, uncomplicated vaginal birth within 24 hours of commencing oxytocin. Typically, the duration of pre-induction cervical ripening with a Foley bulb (mechanical ripening) or prostaglandins or indeed oxytocin (pharmacologic) is variable. The cervical ripening (as applicable) status of the cervix just before the commencement of oxytocin is most predictive of successful vaginal delivery. The principal complication of labor induction is a failed induction and a cesarean section.
Induction of labor represents an opportunity to intervene in an ongoing pregnancy within intent to effect delivery. It represents an essential component of obstetric intervention for the betterment of maternal-fetal outcomes. The methodology for induction of labor is well established. Other than the cervical status there are the non-cervical factors that may impact on the success of induction. Such factors may include gestational age, parity, ruptured membranes (in which case Foley bulb induction and prostaglandin administration are relatively contraindicated), non-obese woman, and adequate placental function.