Clinical:Induction of Labor

Description

The goal of induction of labor is to achieve vaginal delivery through cervical dilation and uterine contractions prior to the onset of spontaneous labor. This is to be distinguished from augmentation of labor, which is the assistance of cervical dilation and or uterine contractions after labor has been diagnosed.

According to the National Center for Health Statistics, over 21.2% of live births involved induction of labor. This represents an over 100% increase from levels in 1990-1991 (9.5-10.5%). Importantly, the increase in clinically indicated induction is not increasing proportionally to the overall induction rate, suggesting that much of the rise in induction rates are due to elective inductions. An elective induction is typically considered as the initiation of labor without an obstetrical or medical indication.

Why Induction of Labor Is Done

In general, induction of labor is indicated when the risks of continuing the pregnancy outweigh the risks associated with delivery. Medical indications for induction of labor include: chronic maternal medical conditions (diabetes, hypertension, renal disease), fetal compromise (IUGR, alloimmunization, abnormal fetal testing), gestational hypertension or preeclampsia, post-term pregnancy, primature rupture of membranes or preterm premature rupture of membranes, placental abruption, chorioamnionitis, or fetal demise. ^[1]

Contraindications to induction of labor include vasa previa or placenta previa, transverse fetal lie, umbilical cord prolapse, previous transfundal uterine surgery, and active genital herpes. ^[2]

Though not absolute contraindications, careful considerations should be made with regard to induction in pregnancies with one or more prior low transverse cesarean delivery, breech presentation, maternal heart disease, multiple gestations, polyhydramnios, severe hypertension, and abnormal fetal heart rate patterns. ^[3]

Labor may be induced for logistical reasons (e.g. a patient with a history of rapid labor, or who lives far from the hospital) or for psychosocial reasons as long as fetal pulmonary maturity is documented or the pregnancy is documented to be 39 weeks' gestation or greater. Macrosomia, pending macrosomia, and history of shoulder dystocia are not credible indications for induction of labor.

How Induction of Labor Is Done

If the cervical exam already shows dilation and shortening, induction is often initiated with oxytocin, an intravenous medication to stimulate contractions.

If the cervix does not show such changes, preinduction cervical ripening is often necessary. Assessment of the cervix is commonly done through use of the Bishop score.^[4] The Bishop score incorporates assessments of cervical dilation, effacement, consistency and position as well as fetal station. According to the original study by Bishop, all patients with a score of 9 or more achieved vaginal delivery, while 50% of patients with a score of 5 or less had a cesarean delivery. Notably, this was before the contemporary age of effective ripening agents.

Preinduction ripening for a cervix with a low Bishop score aims to soften and dilate the cervix prior to the onset of contractions. This can be achieved pharmacologically (with prostaglandin medications, such as misoprostol or dinoprostone, administered vaginally) mechanically (with a transcervical Foley catheter balloon or laminaria).

Transcervical Foley catheter balloon ripening is becoming a more popular form of induction of labor, as it shows similar clinical effectiveness to the prostaglandin agents and there is a lower risk of uterine tachysystole and the associated fetal heart rate abnormalities.^[5]

Some natural methods of induction include membrane stripping during a vaginal exam, amniotomy (rupture of the fetal membranes), nipple stimulation, and intercourse.

Benefits

The benefit of induction of labor is that a trial for vaginal delivery is possible, when delivery is indicated. Without an attempt at induction, cesarean delivery is the only alternative if delivery must be performed prior to the onset of labor.

Risks

Complications

Induction of labor is associated with a 50-100% increase in risk of cesarean delivery when compared to patients going into spontaneous labor. The risk is primarily in patients who are nulliparous and those with an unfavorable cervical exam.

Iatrogenic prematurity is another concern with induction. The incidence of respiratory distress syndrome increases 2-4x if the induction results in cesarean delivery.

Prostaglandin induction of labor is associated with increased risks of uterine tachysystole and fetal heart rate decelerations associated with tachysystole. There is also an increased risk of meconium stained amniotic fluid, and in a patient with a prior cesarean delivery, an increased risk for uterine rupture.

Related problems

Uterine overstimulation (tachysystole) may occur during induction due to the exogenous stimulation of uterine activity. By definition, tachysystole is when there are more than 5 contractions per 10 minutes, when averaged over a 30 minute period. Occasionally tachysystole may have effects on the fetal heart rate patterns.

Oxytocin may be associated with hyponatremia when given in large volumes of hypo-osmolar fluids for prolonged periods.

However, the most obvious problem related to induction is when induction fails. Failure rates will be higher for nulliparous patients. There is no consensus on what defines a failed induction of labor.

Precautions

Side Effects

Medical induction of labor is often associated with hospitalization. Often, particularly when prostaglandins or oxytocin is used, continuous fetal heart rate monitoring is necessary.

Effectiveness

Experts on Induction of Labor

Doctors and specialists

Christian M. Pettker, MD

Other Resources

ACOG Education Pamphlet

References

External Links

American College of Obstetricians and Gynecologists