Best Evidence: Induction of Labor
Best evidence: When making important maternity decisions, women should have information from the best available research about the safety and effectiveness of different choices. In general, we can be most confident about results of systematic reviews that summarize randomized controlled trials (or RCTs, a type of study).
Unfortunately, for many decisions we must rely on less definitive research; and many important questions - even in the case of widely used drugs, tests and procedures - have hardly been studied at all. Although this situation is discouraging, an awareness of weak or missing evidence can help you make informed choices about care.
What is the bottom line about induction of labor?
In what situations does induction of labor improve health outcomes for the mother, baby, or both?
What common "reasons" for induction are not supported by rigorous research?
Which induction method is most effective and safest?
To decide about induction of labor, women need to consider whether the induction is more likely to help or harm them and their babies. Induction of labor is an important option when continuing the pregnancy may be risky for either the baby or the mother because sometimes induction of labor can reduce that risk. Sometimes induction does not work and results in a c-section, or the methods used to induce labor cause complications. It is important to think carefully about the possible benefits and harms of induction of labor, especially if there is not a clear medical reason to induce labor.
The safety and effectiveness of labor induction depend on the health of the woman and her baby, whether she has given birth before, the timing of the induction, the method used, the characteristics of the birth facility, and many other factors. It is difficult to predict the risks and benefits of induction for an individual woman and her baby.
Research suggests that:
- Elective induction (induction without a well-supported medical reason) before 39 completed weeks clearly increases risks for babies. These risks include breathing problems, infection, and admission to a neonatal intensive care unit (NICU). A large amount of brain growth and development happens in the last weeks of pregnancy, and babies born even a few weeks before their due dates have more learning and behavioral problems than babies born after 39 weeks.
- Elective induction before 41 weeks increases the chance of having a c-section if the cervix has not already softened and started to open on its own, especially in first-time mothers.
- Using medications or procedures to soften the cervix does not decrease the chance of a c-section.
- Women in induced labor are more likely to ask for an epidural for pain relief than women who go into labor on their own. Epidurals have their own risks, including increased chance of having a forceps- or vacuum-assisted vaginal delivery and fever in labor. Women who have fevers in labor are often treated with antibiotics and their babies may have tests and treatments and need to be observed in a special nursery. (These and other risks are discussed in greater detail in our Labor Pain section.)
(King and colleagues 2010, a systematic review)
Induction methods also change the type of care and monitoring a woman will need in labor. Induction of labor involves having at least one intravenous (IV) line, continuous electronic fetal monitoring, and medications after birth to reduce the risk of hemorrhage (too much bleeding). The IV and fetal monitoring equipment make it harder to move around in labor, which can increase pain. Many hospitals don’t allow women to eat or drink during induction of labor.
Although decisions about whether and when to induce labor must be individualized, a 2009 systematic review of the research on induction of labor (Mozurkewich and colleagues 2009) found only two conditions for which induction of labor seems to reliably improve health outcomes, and a later study identified a third (Koopmans and colleagues 2009). In all three cases, differences in health outcomes were small and the studies left some important questions unanswered. Thus, women will want to make informed choices about whether to undergo labor induction in these situations:
- Pregnancy lasting beyond 41 weeks: Various studies have compared induction of labor at or after 41 weeks with "watchful waiting" with repeated tests of fetal well-being between 41 and 42 weeks. Taken together, the studies suggest that for every 369 women induced during the week between 41 and 42 weeks, one stillbirth or neonatal death may be prevented. The risk of meconium aspiration syndrome (an illness that causes serious breathing problems) may also be slightly lower. Induction between 41 and 42 weeks does not seem to increase the risk of c-section, and some studies have shown that this reduces the risk.
- Prelabor rupture of membranes (PROM) at term (37-42 weeks): A large randomized controlled trial compared immediate induction with waiting up to three days for labor and only inducing before then if a complication developed. The study found that inducing right away was associated with a lower chance that the mother would develop an infection or the baby would go to the neonatal intensive care unit. Immediate induction did not affect the likelihood of c-section, newborn infection, or other important outcomes. However, most women in the watchful waiting group had vaginal exams before labor began, and those who carried Group B Strep (GBS, a bacteria that may be present in a woman's vagina and raises the risk of infection for the baby) were not given antibiotics to prevent infection. Many caregivers and researchers believe that avoiding vaginal exams until labor started and providing antibiotics to women with GBS might have prevented many infections reported in the trial. These are standard practice in U.S. maternity care settings today.
- Increased blood pressure near the end of pregnancy: High blood pressure that develops in pregnancy may occur without other symptoms or signs (known as gestational hypertension) or with protein in the urine (a more dangerous condition known as preeclampsia). High blood pressure can affect the flow of oxygen to the baby, increase the chance of complications during labor, and lead to rare but very serious outcomes like stroke and seizures.
Researchers studied outcomes of women at or beyond 36 weeks of pregnancy who had gestational hypertension (diastolic blood pressure - generally, the second number in a blood pressure reading - between 95 and 110) or mild preeclampsia (diastolic blood pressure between 90 and 110 and protein in the urine). The study found that inducing labor right away improved maternal outcomes. However, they defined "poor maternal outcome" to include any cases where women developed severe high blood pressure. Very few of these women experienced serious health problems as a result of the blood pressure increase. There were no significant differences in the number of serious problems like seizure, need for intensive care, or postpartum hemorrhage, although the study was too small to show whether there were differences in these uncommon outcomes. There were also no significant differences in newborn outcomes, although a later study showed that neonatal intensive care admission, need for artificial ventilation (a machine to help the baby breathe), low birth-weight, and jaundice were more common the earlier a woman with mild gestational hypertension was induced, with best outcomes in the group induced after 38 weeks (Koopmans and colleagues 2009; Barton and colleagues 2011).
In the randomized controlled trial, women with mild preeclampsia (versus the more mild gestational hypertension), women having their first baby, and those with the least amount of cervical dilation were the most likely to benefit from a policy of early induction. This is most likely because preeclampsia is a more serious condition than gestational hypertension and first-time mothers and those who haven't begun dilating would have remained pregnant longer, providing more opportunity for their condition to worsen.
For a surprising number of conditions, the effectiveness of induction has not been proven (Mozurkewich and colleagues 2009, a systematic review). Yet many women have induced labor with the understanding that they or their babies will benefit. More research is needed to confirm the benefits and harms of induction in these situations:
- Preterm prelabor rupture of the membranes (PPROM): Four studies with a combined total of 389 women with ruptured membranes between 30 and 36 weeks found no difference in important health outcomes between those who were induced right away and those who awaited labor. A new, larger study is currently underway.
- Twin pregnancy: A single, small randomized controlled trial compared routine induction at 37 weeks with expectant management and found no differences in important health outcomes. More research is needed.
- Gestational diabetes requiring insulin: One trial looked at the outcomes of 200 women randomized to be induced at 38 weeks or await labor. Those who awaited labor were more likely to have large babies. There were no differences in health outcomes for the mothers or babies, however. The trial may have been too small to detect these differences.
- Intrauterine growth restriction (IUGR) at term: Two trials involving a combined 683 women found no benefit or harm to induction of labor for suspected IUGR at term. More and larger trials are needed.
- Oligohydramnios (too little amniotic fluid): A single, small randomized controlled trial compared induction of labor with watching fetal wellbeing closely until 42 weeks for women with suspected low amniotic fluid at 41 weeks. The women were healthy and did not have other risk factors or complications. The study found no difference in maternal or newborn outcomes, but was too small to detect some important differences that may exist. No trials of induction for low fluid levels in women with otherwise healthy pregnancies at other gestational ages were found.
For other conditions, the available evidence suggests induction is ineffective, harmful, or both (Mozurkewich and colleagues 2009, a systematic review). Despite the research, many caregivers continue to recommend induction of labor for these reasons. They include:
- Concern that the baby will get too big (suspected macrosomia): According to a systematic review of several studies involving over 3700 women, inducing labor when the caregiver suspects that the baby is large does not improve neonatal outcomes and appears to increase the chance that the woman will have a c-section.
- Intrauterine growth restriction before 37 weeks: A large, multi-center randomized controlled trial of over 1000 women with growth-restricted fetuses between 24 and 36 weeks and abnormal Doppler artery blood flow studies showed that induction increased the likelihood of c-section. In addition, babies born before 31 weeks in the induction group were more likely to have severe disabilities at 2 years of age than babies born before 31 weeks in the await labor group.
It is very difficult to know the safest and most effective way to induce labor in a particular woman. The research provides only a few clear answers because most studies do not compare the different methods to one another. Also, not enough research shows the effects of different combinations of methods used in the same woman.
The best induction method depends on whether you have begun dilating, whether your water has broken, whether you or your baby have health problems, and other factors. Different methods have different risks and benefits. Some risks and benefits are unknown because there is not enough research.
There are many ways women or caregivers may attempt labor induction before going to the hospital. Most of these have not been studied closely. The research that does exist shows (Mozurkewich 2011, a systematic review):
Women who are planning a hospital induction of labor need to decide which methods to use. An important factor in making the decision is the woman's "Bishop score." This score measures the qualities of the cervix and the position of the baby to estimate how ready the woman and baby are for labor. If the Bishop score is 6 or higher, the induction is likely to begin with Pitocin (oxytocin), breaking the bag of water, or both.
- Compared with doing nothing, the following methods do not seem to be effective for starting labor:
- Sexual intercourse
- Sweeping/stripping membranes (an office procedure done with a vaginal exam)
- Breast stimulation increases the likelihood of starting labor, but more research is needed to understand safety (safety concerns involve strong contractions that reduce oxygen flow to the fetus, although the study that raised this concern was done in women with high-risk pregnancies).
- Castor oil is effective at starting labor, but does not decrease the chance of having a c-section. Castor oil causes nausea and diarrhea in most women. More research is needed to understand safety.
If the Bishop score is less than 6, most caregivers will recommend "cervical ripening" to make the cervix soft and ready to open. Three different methods may be used for this:
- Breaking the bag of water may be effective on its own, but once the bag of water is broken the induction cannot be stopped because this increases the risk of infection.
- Pitocin is given by IV line and requires continuous electronic fetal monitoring. If labor does not start, the Pitocin can sometimes be stopped and restarted later if the bag of waters is not broken and the mother and baby are healthy.
- Pitocin and breaking the bag of water may be used together, and this combined method increases the chance of giving birth within 24 hours compared with just breaking the bag of water.
Effectiveness and safety vary (Mozurkewich 2011, a systematic review). All of the methods increase the chance of having the baby within 24 hours, but none reduces the chance of having a c-section compared with inducing labor without these methods. (Misoprostol is a possible exception, but more research is needed.)
- prostaglandin E2 (PGE2), a hormone medicine usually given as a gel, tablet, or tampon inserted in the vagina.
- misoprostol, a different hormone medicine. It comes in pill form and can be given by mouth or inserted in the vagina.
- mechanical methods. The most common mechanical method is a "foley balloon," a balloon that is inserted through the cervix and then inflated so it puts pressure on the cervix from the inside.
PGE2 and misoprostol increase the chance of very strong contractions that can decrease oxygen flow to the baby. Misoprostol causes this problem more often than PGE2, but also works more quickly and may reduce the likelihood of having a c-section. Misoprostol should never be used in women planning a vaginal birth after cesarean (VBAC) because it increases the chance of uterine rupture.
Mechanical methods like the foley balloon are as effective as PGE2 and are less likely than both PGE2 and misoprostol to cause very strong contractions that can decrease oxygen to the baby.
After cervical ripening, the woman will usually have Pitocin and the bag of water will be broken. However, sometimes cervical ripening methods work to induce labor on their own.
Scientists have begun to study new methods of inducing labor. These methods should not be used except in research studies, because they are still experimental:
- Isosorbide Mononitrate
References Barton JR, Barton LA, Istwan NB, et al. Elective delivery at 34(0/7) to 36(6/7) weeks' gestation and its impact on neonatal outcomes in women with stable mild gestational hypertension. Am J Obstet Gynecol. 2011;204(1):44.e1-44.e5..
Boers KE, Vijgen SM, Bijlenga D, et al. Induction versus expectant monitoring for intrauterine growth restriction at term: Randomised equivalence trial (DIGITAT). BMJ. 2010;341:c7087
King V, Pilliod R, Little A. Rapid review: Elective induction of labor.
Portland: Center for Evidence-based Policy; 2010 Accessed January 5,
2011 at http://www.ohsu.edu/xd/research/centers-institutes/evidence-based-policy-center/med/index.cfm.
Koopmans CM, Bijlenga D, Groen H, et al. Induction of labour versus expectant monitoring for gestational hypertension or mild pre-eclampsia after 36 weeks' gestation (HYPITAT): A multicentre, open-label randomised controlled trial. Lancet. 2009;374(9694):979-988.
Mozurkewich E, Chilimigras J, Koepke E, Keeton K, King VJ. Indications for induction of labour: A best-evidence review. BJOG. 2009;116(5):626-636.
Mozurkewich E, Chilimigras JL, Berman DR, Perni UC, Romero VC, King VJ, Keeton KL. Methods of induction of labour: a systematic review. BMC Pregnancy and Childbirth. 2011; 11(84):1-19.
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Most recent page update: 1/24/2012