Is Routine Induction at 41 Weeks Superior to Expectant Management?

For some time, it has been taken as established fact that routine induction at 41 weeks reduces perinatal mortality while not increasing—and probably decreasing—cesarean rates. Three years ago, I did a guest post for Lamaze examining whether the research on those points was as indisputable as it was thought to be. I reviewed the research with an eye to answering two questions: (1) “Does routine induction at 41 weeks reduce perinatal mortality rates (deaths around the time of birth)?” and (2) “Does routine induction at 41 weeks affect cesarean rates?” In this new post, I will revisit those same two questions.

I’ll start by summarizing my findings in the earlier post—you can get the details by clicking over to the Lamaze post—and follow that with an analysis of the studies that have accumulated since. As usual, I’ll wrap up with a take-away section giving you suggestions for practical application of my findings.

Does Routine Induction at 41 Weeks Reduce Perinatal Mortality?

Summary of the Lamaze Post

The conclusion that induction at 41 weeks reduces perinatal mortality came largely from a series of systematic reviews (studies pooling data from multiple studies) on that topic published by the prestigious Cochrane Library, a database of systematic reviews of randomized controlled trials (studies in which participants are assigned by chance to one form of treatment or another). The earliest in the series was published in 1996,⁵ and the Cochrane Library has issued updated versions thereafter as more trials were published. The version I reviewed in the Lamaze post was published in 2018,²³ and it, as had its predecessors, concluded that routine induction reduced perinatal mortality compared with expectant management.

In rebuttal to this, I offered Rydahl and colleagues,³⁵ who authored a systematic review that begged to differ from this conclusion. They pointed out that the Cochrane reviews had never answered the pertinent research question, which was: Does routine induction in the 41^st week in uncomplicated pregnancies in a contemporary medical system reduce preventable perinatal deaths? Unlike the 2018 Cochrane review, their review restricted studies to those published within the last 20 years that compared routine induction at 41 weeks + 0-6 days versus routine induction at 42 weeks in uncomplicated pregnancies, and they excluded deaths unrelated to the timing of labor. They reported a much smaller difference between perinatal mortality rates with routine induction versus expectant management, one that was not statistically significant, meaning that probabilities calculation showed that it could have been due to chance.

In addition to the opposing reviews, my Lamaze post covered two trials, one conducted in Sweden and the other in the Netherlands, that were published the year after the 2018 Cochrane review.^{16, 39} The trials likewise reported contradicting results for the same reason as the two reviews: one of trials didn’t meet Rydahl’s criteria for determining whether routine induction at 41 weeks in uncomplicated pregnancies reduced perinatal mortality. The Swedish trial, which concluded that it did, included one death in the expectantly managed group that couldn’t have been prevented by 41-week induction (heart defect) and a second one in a baby who was small for gestational age (usually defined as weighing in the 10^th percentile or lower for gestational age), which would remove the pregnancy from the low-risk category.³⁹ The Dutch trial, by contrast, reported similar rates in the induced and expectantly managed groups.¹⁶

Finally, I reported on two studies that evaluated the effect of the increased prevalence of induction at 41 weeks on perinatal mortality. One of them critiqued a study concluding that a change in induction policy from routine induction at 42 weeks to induction in the 41^st week had reduced stillbirths in Denmark.³⁴ The critics pointed out that the stillbirth rate in Denmark had been declining prior to the change in policy and that projecting the same rate of decline forward would produce the same stillbirth and perinatal mortality rates as were being attributed to the change in induction policy. In the other, Finnish investigators conducted a propensity study, a study design in which investigators match large numbers of participants according to so many factors that each pair differs only in that one member of the pair received the treatment under study and the other didn’t.³² They divided the time between 40 and 42 weeks into five 3-day periods and compared outcomes with induction within each time period with ongoing pregnancy after that period. They found that induction had no effect on perinatal mortality.

Analysis of the New Studies

Since the Lamaze blog post, yet another iteration of the Cochrane review has been published.²⁴ The update included the Swedish and Dutch trials discussed above plus a trial that assigned first-time mothers with uncomplicated pregnancies to either induction at 39 weeks or expectant management.⁹ As we saw in my summary of the Lamaze post, the Swedish trial suffers from some of the same flaws as others in the Cochrane review, and the 39-week induction trial has its own problems. (If you want to know more about them, see my post: “Parsing the ARRIVE Trial: Should First-Time Parents Be Routinely Induced at 39 Weeks?”)

This latest version of the Cochrane review reports 25 perinatal deaths among the 9377 participants assigned to expectant management (25 per 10,000) versus 4 perinatal deaths among 9418 participants assigned to induction (4 per 10,000). That sounds pretty definitive, but let’s see what happens when we restrict the results to those that meet the parameters of Rydahl’s research question plus one additional criterion: the study was conducted in a high-resource country. I’m adding this one because management and outcomes in low- and medium-resource countries might not be generalizable to high-resource countries. That makes our new question:

Does routine induction . . .

1. in a contemporary medical system,
2. in a high-resource country,
3. in the 41^st week,
4. in uncomplicated pregnancies,
5. reduce preventable perinatal deaths?

When we look at deaths that meet these criteria, perinatal mortality rates with expectant management fall from 25 per 10,000 (25/9377) to 6 per 10,000 (5/7776), and rates with routine induction decline from 4 per 10,000 (4/9418) to none in 7772. Five deaths with expectant management are a long way from 25, and a perinatal mortality rate of 6 per 10,000 is a number so small that the difference compared with routine 41-week induction may well be due to chance. (For details, see “Taking a Deeper Dive” below.)

In addition to the updated Cochrane review, another study has been published that explores the effect of a change in induction policy on perinatal mortality, this time in Norway.¹¹ The study included all singleton births between 37 and 43 weeks from 1999 through 2019, which means they weren’t necessarily low-risk pregnancies. The induction rate increased markedly over the time period, especially in week 41. The increase had no effect on newborn mortality, and while fetal deaths decreased from 18 per 10,000 to 13 per 10,000, two-thirds of the decline were in pregnancies between 37 and 40 weeks of gestation. In other words, the increase in 41-week induction had a negligible effect on perinatal mortality—and that was in a population that included moderate and high-risk pregnancies.

Conclusion

Putting the old and the new data together, the conclusion that routinely inducing low-risk pregnancies at 41 weeks reduces perinatal mortality has been on shaky ground from the beginning, and new studies have further undermined it.

Does Routine Induction at 41 Weeks Affect Cesarean Rates?

All that being said, it could still be argued that you can’t have an antenatal death between week 41 and 42 if the baby is delivered at the beginning of week 41, so it comes down to whether routine induction has counterbalancing harms, in particular, whether it increases the likelihood of cesarean delivery. If it does, then this must be weighed against the possibility of averting a stillbirth because cesarean surgery increases the probability of severe and life-threatening complications in subsequent pregnancies, including miscarriage¹⁵ and stillbirth.^{1, 25, 28} As before, I’ll start with a summary of the Lamaze post data on cesareans followed by an analysis of studies that have been published since.

Summary of the Lamaze Post

The reviews and trials I analyzed in the Lamaze blog post varied in their findings of the impact of 41-week induction on cesareans. The Swedish and Dutch trials reported no difference, the Cochrane review found a reduction of 1 percent with induction, and the Rydahl review found an increase of 2 percent.^{16, 23, 35, 39}  Based on these studies, it would appear that the effect of 41-week induction is unclear but modest at best. There were other studies, though, finding that the impact was neither benign nor minor.

Two studies evaluated the effect of a change in induction policy on cesarean rate. A Spanish study in a mixed population of first-time mothers and those with prior vaginal births looked at the effect of changing the timing of routine induction from 42 weeks to 41 weeks.⁴ The cesarean rate increased from 11 percent to 14 percent. A U.K. study of first-time mothers looked at a change in the other direction: from 41 weeks 3 days to 42 weeks.¹⁴ The restriction to first-time mothers is important because they are much more vulnerable to factors that affect labor progress than women with previous vaginal births. The shift to later induction dropped the cesarean rate from 33 percent to 24 percent.

Three studies looked at the effect of routinely inducing labor in week 41. The first, of first-time mothers, found that the cesarean rate was 22 percent with induction versus 12 percent when labor started on its own.²¹ The second, also of first-time mothers, compared rates between women induced as planned during week 41 with women who began labor spontaneously during that week either because they started labor before their induction date or induction wasn’t planned until week 42.³¹ The cesarean rate was 25 percent with induction versus 17 percent when labor started on its own. The third study found that even shifting the timing of planned induction from early to late in week 41 had a profound effect on the percentage of women induced (92 percent vs. 37 percent) and on cesarean rates (31 percent vs. 20 percent).²⁹

Analysis of the New Studies

Since the Lamaze blog post, in addition to the updated Cochrane review,²⁴ which again reported a small decrease in cesareans with induction (16 percent vs. 19 percent), two new studies have been published that investigated induction’s effect on cesarean rate. A French study looked at cesarean rates with induction versus spontaneous labor onset in first-time mothers who reached 41 weeks with a cervix unfavorable for labor (Bishop score of 3 or less).²² French policy is to induce for medical indications or maternal preference between 41 weeks 0 days and 41 weeks 4 days and to induce everyone who hasn’t yet given birth at 41 weeks 5 days. Thirty-eight percent of the women started labor on their own between 41 weeks 0 days and 41 weeks 5 days. Among women starting labor on their own, the cesarean rate was 20 percent versus 41 percent in women who were induced. The other study, this one of first-time mothers in the U.S., looked at cesarean rates with induction versus spontaneous labor onset in each week from week 39 through week 41.²⁰ In week 41, the rates were 39 percent with induction versus 25 percent if labor started on its own.

Conclusion

Again, combining the studies in the Lamaze post with those that have been published since, we have ample evidence that 41-week induction markedly increases probability of cesarean surgery, at least in first-time mothers.

As to why the trials and systematic reviews of trials didn’t find a major difference while these other studies did, at the top of the list is that the trials were in mixed populations of first-time mothers, who are much more vulnerable to factors that affect labor progress, and women with prior vaginal births, who are almost certain to birth vaginally, induced or not. Their presence would mask induction’s adverse effect on first-time mothers. Another contributing factor may be that outcomes in studies conducted in the tightly-regulated, hothouse conditions of randomized controlled trials may differ from those under real world conditions in typical hospitals with typical care providers. Finally, some studies were conducted in countries where overall cesarean rates were much lower than in others. The cesarean mindset, as it were, could affect judgment on when to proceed to cesarean.

The Take-Away

As we have seen, the choice isn’t anything like as clear as it has been made out to be. Because your choice depends on your individual circumstances, I’ve organized my suggestions according to whether you’d like to avoid routine induction at 41 weeks, or you want to plan an induction and maximize your chances of having an uneventful vaginal birth.

If you would prefer to avoid routine induction before 42 weeks, here are some ways that may help you determine with your care provider whether you’re a good candidate for expectant management:

• Late-pregnancy ultrasound scan to confirm uncomplicated pregnancy. Despite congenital anomalies being an exclusion factor in both the Swedish and Dutch trials, one intrapartum death occurred in a baby with an undiagnosed heart defect in the Swedish trial,³⁹ and in the Dutch trial,¹⁶ 6 of the 11 children admitted to neonatal intensive care had a severe congenital anomaly. Two of the deaths, one in each trial, occurred in babies who were small for gestational age. We don’t know, of course, whether induction would have made a difference in outcome in these cases, but it’s something to factor into a decision.
• Prenatal testing to evaluate fetal wellbeing. In point of fact, systematic reviews of the various prenatal fetal surveillance tests have failed to find benefit,^{8, 17, 26, 27} but considered thoughtfully and as part of an overall picture, they may still prove of use. Using the biophysical profile, which measures more than one parameter, or repeating a test or doing a different test if the result suggests there’s a problem reduces the probability of a false-positive result. A single finding that slightly deviates from normal may not be concerning but finding an increasing trend in the wrong direction with serial testing or finding it in combination with other suboptimal maternal or fetal factors would be more worrisome.

If you opt for induction, here are some induction management options to discuss with your care provider:

• In the absence of an acute medical problem, wait for a favorable cervix. Studies consistently find that inducing first-time mothers with an unfavorable cervix substantially increases the likelihood of cesarean despite use of cervical ripening agents whereas inducing with a cervix that is ready for labor does not.^{6, 7, 18, 19, 38}
• If the cervix is favorable, go straight to oxytocin. Cervical ripening agents aren’t necessary and omitting them avoids the possibility of experiencing their adverse effects.
• The oxytocin protocol should “start low & go slow.” Equally high vaginal birth rates can be achieved with fewer adverse effects than with more aggressive regimens.^{3, 10} The Pitocin package insert includes a recommended regimen.
• Refrain from rupturing membranes before active labor. If membranes are intact and the induction isn’t working, it can be stopped and tried another day. Once membranes are ruptured, that’s no longer an option, which means increased probability of cesarean for induction failure.
• Turn off the oxytocin drip once labor reaches active phase. If it doesn’t, the drip can always be turned back on.³⁶ Discontinuing oxytocin decreases likelihood of abnormal contractions and abnormal fetal heart rate and increases likelihood of vaginal birth.¹³
• Have patience. Induced labors tend to take longer than labors that start on their own,^{2, 12, 30, 33, 37, 38} especially in first-time mothers, but longer labors don’t result in worse maternal or newborn outcomes.^{2, 37}

Taking a Deeper Dive  

As promised above, here are the specifics of how the numbers change when you restrict the Cochrane review’s results to those that answer the relevant research question:

Does routine induction . . .

1. in a contemporary medical system
2. in a high-resource country,
3. in the 41^st week,
4. in uncomplicated pregnancies,
5. reduce preventable perinatal deaths?

The starting point for perinatal mortality rates in the Cochrane review is:²³

• Expectant management: 25/9377 = 25 per 10,000
• Routine induction: 4/9418 = 4 per 10,000

If we exclude studies not conducted in high-resource countries (Thailand, India, Tunesia, Turkey) and studies that may not represent contemporary care (pre 1990), the rates become:

• Expectant management: 14/7776 = 18 per 10,000
• Routine induction: 3/7772 = 4 per 10,000

If we eliminate deaths occurring before 41 weeks and stillbirths where the timing of demise is unknown, that is, deaths that couldn’t (or probably wouldn’t) have been prevented by induction at 41 weeks, the numbers become:

• Expectant management: 9/7776 = 12 per 10,000
• Routine induction: 0/7772 = 0 per 10,000

If we eliminate deaths that weren’t in low-risk infants (small for gestational age), the rate in expectantly managed pregnancies falls to:

• Expectant management: 7/7776 = 9 per 10,000
• Routine induction: 0/7772 = 0 per 10,000

Finally, if we eliminate deaths that were not preventable (heart defect, true knot in the umbilical cord), the final numbers are:

• Expectant management: 5/7776 = 6 per 10,000
• Routine induction: 0/7772 = 0 per 10,000

To repeat what I said above, 5 deaths with expectant management are a long way from 25, and a perinatal mortality rate of 6 per 10,000 is a number so small that the difference compared with routine 41-week induction may well be statistically insignificant.

References

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