Routine 39-Week Induction: Busting the ARRIVE Trial

by | Oct 15, 2023 | Induction of Labor

“‘Enkins First Law’: The RCT [randomized controlled trial] is perfectly designed to show the results for the conditions under which the RCT is conducted—BUT only for those conditions.”35

For this month’s blog post, I decided it was time to update my critique of the ARRIVE trial.28 This is the study that is single-handedly responsible for the notion that routine induction at 39 weeks is better for healthy women and birthing people having first babies than allowing the pregnancy to continue longer because induction reduced the odds of cesarean. Among the more recent studies and commentaries, I discovered a bombshell: a secondary analysis of the ARRIVE trial’s data that provides incontrovertible proof that the 39-week induction group had fewer cesareans because of how the expectantly managed group was managed.48 With optimal care, expectant management would have been much the better option.

You can take that as my teaser because we need to cover some other ground first before we dive in.

Here’s the setup: I’ll start by busting the myth that inducing labor doesn’t increase cesareans. Next, I’ll give you the backstory of how we got to a place where routine induction in the absence of any reason to do so was deemed superior to letting nature take its course. After that, I’ll take you through what the secondary analysis revealed about why routine 39-week induction looked better when it really wasn’t. Finally, I’ll wrap up, as usual, with your takeaway: practical ideas about what you can do with what you’ve learned. This is going to be a long one so relax and settle in with the beverage of your choice.

Busting an Induction Myth

Before I can discuss the ARRIVE trial, I need to bust the myth that induction doesn’t increase cesareans. Obstetricians have long clung to that belief in the face of the evidence because it enables them to practice what in the 1950s was called “daylight obstetrics”: “Scheduling an induction can make everyone’s life easier,’ [Dr. Leveno] said. . . . ‘I am not capable of constantly doing my best work in the middle of the night.’”53

When questions were first raised about induction increasing cesareans, obstetricians responded that any observed increase in cesareans was due to the inductions for medical indications that were in the mix. But a long list of studies consistently showed an increase in cesareans with elective induction, that is, induction that wasn’t for a medical indication, especially at first births. Anywhere from 3 to 31 more first labors per 100 will end in cesareans with an elective induction compared with labors that started on their own.4, 8, 10, 17, 20-22, 30, 41, 42, 47, 49, 51, 52 Furthermore, If induction for medical indication was why inducing labor resulted in more cesareans, we would expect to find higher cesarean rates in inductions for these reasons than in electively induced labors, but we don’t. We have several studies that report similar cesarean rates in labors induced electively and labors induced for medical reasons.4, 47, 54 We even have one that reported higher cesarean rates with elective induction than in inductions for medical reasons.27 We also have a study looking at what factors are associated with induced labor ending in cesarean and the strength of their association.34 That study found that having a medical indication for induction played a minimal role in whether the labor ended in cesarean.

Obstetricians countered that factors other than medical complications can make both induction and cesarean delivery more likely, and this explains why studies of elective induction report higher cesarean rates. But chief among these factors is birthweight. All of the studies I just cited accounted for the effect of birthweight and still found an increase in cesareans with induction.

Undiscouraged, obstetricians next argued that It isn’t a simple question of comparing induced labors with labors that started spontaneously. Because we know the cesarean rate increases as pregnancy advances, their argument ran, the clinical management question is: are pregnancies reaching term (37 weeks, the point at which the baby is considered to be mature) less likely to end in cesareans with induction compared with allowing the pregnancy to continue to some later date?11 They then pointed to studies that compared induction in each week after reaching term with continuing the pregnancy beyond that week, which could mean either spontaneous labor onset or induction after that week, and most—although not all46—reported fewer cesareans with induction in that week compared with pregnancies allowed to continue beyond that week.12, 16, 39 But comparing induction in a particular week with pregnancies allowed to continue after that week leaves out pregnancies in which labor began spontaneously during that week. If you include these pregnancies in the calculation, cesarean is more likely with induction.3, 16, 24, 25

Their ultimate argument is that inducing before the cervix was ready for labor was what led to an excess of cesareans in the past, and this problem has been solved by administering cervical ripening treatment. But studies consistently find that cervical ripening treatment doesn’t make a difference. Studies report anywhere from 15 to 24 more cesareans per 100 first labors if induced with an unfavorable cervix compared with spontaneous onset despite cervical ripening treatment.21, 37, 38, 49

You can take it as read, then, that inductions increase cesareans at first births, although in fairness I should add that the studies finding that cervical ripening doesn’t eliminate excess cesareans also found that inducing when the cervix is ready to go on its own results in similar cesarean rates to spontaneous onset. You can also take it as read that obstetricians are not going to give up their belief that inductions are harmless despite the facts, and that belief will influence the practices of any clinician who holds it and color the design, implementation, and interpretation of any research into induction.

The Backstory

We’re still not quite ready to tackle the ARRIVE trial. I first want to give you some context because the ARRIVE trial didn’t arise in a vacuum.

The last few decades have seen an ever-lengthening list of rationales for inducing labor—postdates, predicted big baby, older maternal age, high BMI— that aren’t elective, as in “inductions for the sake of convenience,” but aren’t medical indications either. These rationales fall in a gray area of “precautionary inductions”: inductions recommended to end healthy pregnancies that are proceeding normally with the intent of averting an adverse outcome that may or may not arise in the future. Precautionary indications justify inducing problem-free pregnancies on the grounds that it will improve outcomes. With the ARRIVE trial, that trajectory culminated in adding everyone expecting a first baby to the list.

Briefly, the ARRIVE trial, published in 2018, randomly assigned 6,100 healthy women and birthing people having a first baby to either induction at 39 weeks—a date chosen because earlier induction is associated with increased respiratory complications in newborns—or to “expectant management,” which meant until either labor began spontaneously, was induced, or the trial participant underwent planned cesarean.28 Compared with expectant management, routine induction decreased cesarean rates from 22% to 19%—3 fewer cesareans per 100 routinely induced labors—and similar percentages of newborns experienced one or more of a constellation of adverse outcomes or were admitted to an intensive care nursery.

Finding fewer cesareans and similar newborn outcomes in a large, multicenter randomized trial provided strong support for routine induction at 39 weeks for all first births, and pressure has been ratcheting upward ever since that this should become the norm. One of the two pre-eminent U.S. obstetrics journals went so far as to run an editorial under the title “39-week nulliparous [first birth] inductions are not elective.”23 (Sidenote: Making induction for precautionary reasons the norm has occurred—or is occurring—for all the rationales I listed above. In particular, “pregnancy duration of 41 weeks” is now widely considered a medical indication for induction, despite it being the median length [half of births before and half after a particular value] of healthy first pregnancies,43 despite 42 weeks still being the official demarcation line for “postterm” pregnancy,1 and despite flaws in the research backing 41-week induction.)

So, what’s wrong with this picture?

Busting the ARRIVE Trial

The ARRIVE trial has been deservedly criticized, including by me, on any number of grounds. I won’t go through the list—you can follow the link to my blog post if you’re interested—but before we get to the meat of what I want to add to the criticisms, I’d like to focus on one that addresses the foundational premises of the trial rather than the details of its conduct, and it is this:

The ARRIVE trial was conducted in a medical management environment with medical management practitioners. The premise of the medical approach is that pregnancy and childbirth are perilous, and the care provider’s job is to prevent poor outcomes by managing pregnancy and labor to avert the dangers. But there is an alternative approach: physiologic care, whose premise is that pregnancy and childbirth are healthy, normal experiences for most women and birthing people and their babies. It follows from this premise that the best outcomes will be achieved by promoting and facilitating the unfolding of the natural process and reserving medical intervention for times when these measures prove inadequate.

Studies show that the physiologic approach is the clear winner for reducing cesareans without compromising newborn outcomes. One critic points out that in the ARRIVE trial, 28 inductions were required to prevent one cesarean, but the same benefit can be achieved by providing continuous one-on-one support in 14 labors.14 In other words, providing continuous labor support in 28 labors would prevent two cesareans compared with induction preventing only one. And as I have written, studies of freestanding—that is, not inside hospitals—birth centers and home births report cesarean rates ranging from 5% to 13% at first births in women and birthing people at similarly low risk to those in the trial, or 6 to 14 fewer cesareans per 100 than the 19% rate the trial reported with induction at 39 weeks.2, 6, 7, 9, 29, 31-33, 45, 50

I’ll add, too, that while additional studies since the ARRIVE trial’s publication have also concluded that routine induction reduced cesareans—although others have disagreed15, 19, 40—these studies were conducted according to the medical approach as well and would therefore suffer from the same flaw as the ARRIVE trial.

And now, finally, we’ve arrived (pun intended) at the new news I want to talk about in this post.

A crucial question not answered in the 2018 report on the ARRIVE trial is: “What percentage of participants in the expectant management arm of the ARRIVE trial were induced?” That’s a money question because as we saw above, induction greatly increases cesarean rates at first births, which means that if a large percentage of the expectant management arm was induced, you wouldn’t see a benefit of expectant management that you would see if that weren’t the case.

We now have a secondary analysis of outcomes in the expectant management arm (2,502 participants) of the trial that answers that question.48 The study authors think their analysis affirms that 39-week induction is the superior option, but hidden in plain sight are data that contradict that conclusion. Follow along with me to see how participants would have been much less likely to have cesareans had expectant management actually meant “waiting for labor to start on its own barring a clearcut medical reason to end the pregnancy.”

To recap, the ARRIVE trial reported that the cesarean rates among ultra-low-risk participants having a first baby were 19% with 39-week induction (all but 6% were induced as planned during week 39) versus 22% with expectant management.28

ARRIVE Trial: Cesarean rates 39-week induction vs. expectant management

However, as I suspected, a substantial percentage (37%) of the expectant management participants were induced. When we break down cesarean rates in the expectant management arm according to whether labor was induced versus labor starting spontaneously, we see that the cesarean rate with induction was more than double the rate with spontaneous onset. My theory was correct. Whether expectant management looks better or worse than routine induction at 39 weeks depends on the percentage who were induced. The higher the percentage who began labor spontaneously, the better expectant management looks.

ARRIVE trial: Expectant management cesarean rates induction vs. spontaneous onset

The secondary analysis also allows us to compare cesarean rates with induction versus spontaneous onset week-by-week in the expectant management group. (The chart ends at 41 weeks because all participants were delivered by 42 weeks 2 days, and seeing as only 427 of the 2,502 made it into the 41st week, there was probably not more than a handful that reached 42 weeks.) As you can see, the pattern is consistent. In every week, cesarean rates are substantially lower in labors that started on their own compared with induced labors.

Of special note is that the cesarean rate with routine induction at 39 weeks was 19%. If participants in the 39-week induction arm had been permitted to begin labor on their own in week 39, among those who did, 12%, or 7 fewer per 100 compared with routine induction, would have had a cesarean.

ARRIVE trial: Expectant management cesarean rate week-by-week induction vs. expectant management

There’s still more. Participants who began labor spontaneously in the expectant management arm would be those who had no complications because otherwise they would have been induced. In other words, they would have been eligible for birth at home and in freestanding birth centers. As the bar graph shows, cesarean rates in labors that began spontaneously were 12% in week 39, 17% in week 40, and 30% in week 41. Apart from week 39, cesarean rates in the ARRIVE trial’s expectantly managed population who began labor spontaneously considerably exceeded rates reported in home and birth center births, which, as I said above, ranged from 5 to 13%. And while I don’t have week-by-week data for any of the home or birth center studies, it’s a safe bet that the rate in week 41 in those studies wasn’t anything like 30%.

However, we still need to determine whether those inductions were justified because if they were, the conclusion that routine induction at 39 weeks is the better option stands. Fortunately, the secondary analysis of the ARRIVE trial also tells us why participants assigned to expectant management were induced.48 The authors categorize their list of reasons for induction and the percentage induced for that reason under “Medically Indicated Delivery,” so they clearly think a high rate of inductions with expectant management is inevitable. Is it? Here’s the list:

  • 48% postdates
  • 13% prelabor release of membranes
  • 16% hypertension
  • 8% reduced amniotic fluid volume (oligohydramnios)
  • 10% non-reassuring fetal status
  • 9% other medical reason

Topping the list, 48%—that’s half—of the “medically indicated” inductions in the expectant management group were inductions at 40 or 41 weeks for postdates. As I said above, the research underpinning the belief that routine induction at 41 weeks meaningfully reduces stillbirths and newborn deaths and has no effect on cesareans is flawed. In this blog post, I contend that the difference in preventable deaths with routine induction in an uncomplicated pregnancy in the modern era in a high-resource country is so miniscule that it may be due to chance, and the increase in probability of cesarean at first births is substantial.

Next is the amniotic sac releasing before labor begins. This is another instance where induction can be safely avoided, although to be fair, induction for this reason isn’t associated with an increased probability of cesarean.

Hypertension, reduced amniotic fluid volume, and non-reassuring fetal status would seem to be unequivocal medical indications for induction, but even these are iffy.

Looking at hypertension, a study reported that, in contrast to the ARRIVE trial, only 5% of healthy women and birthing people developed hypertension with pregnancy duration of 39 weeks or more.3 What could explain finding triple that rate in the ARRIVE trial? One possibility is creative diagnostic coding. A study found that over half of inductions for hypertension did not fulfill the criteria for this diagnosis.13 Coding a woman with mildly elevated blood pressure as “hypertensive” would provide an unimpeachable reason for obstetricians who prefer to induce. As for non-reassuring fetal status, the vast majority of babies that fetal wellbeing tests say are in trouble, are actually fine. Systematic reviews (studies pooling data from multiple studies of the same topic) of the commonly used tests for evaluating fetal wellbeing (non-stress test, biophysical profile, fetal movement counting) all conclude that they don’t reduce stillbirths or newborn deaths in healthy pregnancies, but they increase inductions and cesareans.5, 26, 36 Ditto for reduced amniotic fluid volume.44

So, were all those inductions necessary?

To compare with physiologic care, the induction rate in the ARRIVE trial’s expectant-management arm was 37%. A large study of Medicaid beneficiaries who received care at freestanding birth centers reported a 4% rate in uncomplicated pregnancies.33 This was in a mixed population of those having a first birth and those with prior births, but while it is likely that the rate was higher than 4% at first births, I doubt it was anything like 37%.

To sum up, here’s what the secondary analysis adds to criticisms of the ARRIVE trial: the reason the ARRIVE Trial found that fewer ultra-low-risk pregnancies ended in cesarean with routine induction at 39 weeks was because so many of those assigned to expectant management had inductions, which greatly increased their likelihood of cesarean, and contrary to the opinion of the medical model practitioners who managed ARRIVE trial participants, most of those inductions were unnecessary.

Conclusion

“Our evidence suggests that mainstream obstetric science follows mainstream obstetric practice. A patient and expectant approach to birth…where all is considered normal until proved otherwise, produces a science that proves intervention to be unnecessary. Alternatively, an aggressive approach to birth…, where birth is regarded as normal only in retrospect, generates a science that demonstrates the need for monitoring and intervention.”18

The lowest cesarean rates and best outcomes will be achieved in a model of care that supports the physiologic process and reserves induction for circumstances when the benefits of inducing outweigh the risks. The ARRIVE Trial secondary analysis unwittingly documents that the medical management approach abysmally fails its intended goal of safe, healthy births for women, birthing people, and babies.

Your Takeaway

As we have seen, if you give birth in a typical medical management hospital attended by typical medical management practitioners, you are rolling dice that are heavily loaded against your having a birth that doesn’t involve medical interventions that could have been avoided and their consequent harms. This last section will give you my suggestions for how to prevent that.

Topping the list is choosing a location for birth conducive to physiologic care and care providers who take that approach.

If your pregnancy is healthy, your best bet is to plan birth at home or at a freestanding birth center. In the U.S., choose a midwife who is certified by either the  American Midwifery Certification Board or the North American Registry of Midwives. The former will have CNM or LM after their name, and the latter will have CPM. Here are some questions to ask of potential care providers:

  • (For direct-entry midwives) What is your training and experience?
  • Do you have any specialty skills or knowledge?
  • What are your eligibility criteria for birth outside of a hospital?
  • What happens if I develop a complication during pregnancy?
  • (For home births) What happens if you have more than one woman in labor at the same time?
  • When would you recommend or require transfer to a hospital during or after the birth?
  • What is your arrangement to transfer care if I or my baby develops a complication during labor or after the birth?
  • Would you still be able to accompany me or participate in my care if I require transfer to hospital care?
  • What are your capabilities for handling urgent situations such as heavy bleeding or a baby having trouble breathing?
  • Is your care covered by insurance?

But what if a birth center or home birth isn’t a viable option for you? Here are some questions to ask when choosing a hospital and hospital-based care providers:

  • Questions to ask in choosing a hospital:
    • What is the hospital cesarean rate?
    • What is the general opinion of doulas?
    • What is the hospital’s fetal monitoring policy? What if I want the nurse to listen intermittently?
    • What’s the percentage who have epidurals? What comfort measures and assistance are available if I want to avoid pain medication?
    • How do you facilitate mobility and positioning in labor?
    • What is your policy around eating and drinking in labor?
    • What is your policy for IVs?
  • Questions to ask when choosing a care provider (Tip: Midwives are more likely to, but don’t necessarily, provide physiologic care):
    • Under what circumstances would you recommend a cesarean?
    • What percentage of the women in your care have a cesarean?
    • How do your practices and policies promote vaginal birth?
    • Do all doctors/midwives in your practice have similar policies and practices to yours? If not, how can I ensure that I will be attended by someone who does or that the person who attends me will abide by agreements that we may make?

Whatever your choice of birth location and care provider, consider hiring a doula and take a childbirth education class. Here are some considerations when choosing those:

  • Choose a doula who:
    • is independent from the hospital.
    • is certified.
    • aligns with your views on epidurals.
    • is non-judgmental.
    • has good chemistry with you and your intimate partner.
  • Take a childbirth education class that:
    • is independent from the hospital.
    • is taught by a certified teacher.
    • prepares you to be a full participant in decisions about your care.
    • trains you to cope with labor using non-drug strategies.
    • has something on the order of 10 to 12 hours of classes spread out over several weeks.
    • has 4 to 10 couples.

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