For people with healthy, low-risk pregnancies, water births are associated with better outcomes overall than non-water births. That’s according to Oregon State University researchers who have conducted the largest study of water births to date. Right now, birthing centers offer water birth options, but many hospitals will not allow people to give birth in the water due to liability concerns. The OSU researchers are hoping their study will lead hospitals to change their policies. OSU Assistant Professor of Epidemiology Marit Bovbjerg and OSU Professor of Medical Anthropology Melissa Cheyney join us to discuss their research.

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The following transcript was created by a computer and edited by a volunteer.

Dave Miller: From the Gert Boyle Studio at OPB, this is Think Out Loud. I’m Dave Miller. For people with healthy low-risk pregnancies, giving birth in a tub of water leads to better outcomes overall than non-water births. That’s according to a new study by Oregon State University researchers, the largest ever study of water births. Marit Bovbjerg is an assistant professor of epidemiology at OSU. Melissa Cheyney has been a midwife for 20 years. She’s a professor of medical anthropology there. They both join us now to discuss their research. Welcome to Think Out Loud.

Marit Bovbjerg: Thanks for having us.

Miller: Marit Bovbjerg, first. Why did you want to do this study?

Bovbjerg: This is a follow up of a study we published in 2016 that showed much the same outcomes. But this time we were able to have a bigger sample size which always helps in research. And we were able to use better statistical methods. So we think this one is even more conclusive than our previous effort.

Miller: Before we get to the actual analysis here and the way you used data to find out an answer to your question, maybe Melissa Cheyney, you can describe what we’re actually talking about here. What is a water birth?

Cheyney: Yes. So many hospitals in the US offer warm water immersion for labor as a way to manage pain. And so what’s really in question here is whether it’s safe for the person to stay in the water and actually push the baby out in the water. Why this matters is that service users really want options around pain management and some want options that are not simply pharmacological. So something other than an epidural, so perhaps continuous physical support from a doula or warm water immersion. And the other thing is it’s an unpopular request to ask people to get out of the water after they’ve been laboring there and it’s getting time to push. This is largely driven by consumer demand, but also really wanting to know what kind of safe options there are out there for people who are looking for help managing the pain of labor.

Miller: So Marit Bovbjerg, my understanding is you had a relatively straightforward question: Are water births safe and and how do outcomes for water births compared to births, not in a tub of water, but I get the sense that it wasn’t simple to get a statistically meaningful answer to that question. What were the challenges in the actual research you had to do?

Bovbjerg: Great questions. The first challenge is getting enough people. When you’re doing clinical research, you need a large sample size usually, especially if you’re looking at rare outcomes. One of the things that people are concerned about with water births, of course, is that the baby would die because of drowning or whatever, and that doesn’t happen very often. Most babies in the US don’t die. So you need a huge sample size in order to get a few events like that. Getting a big enough sample is part of the problem, especially because as Melissa said, many hospitals in the US don’t actually offer water births even if they offer water immersion during labor, they ask people to get out of the tub before they start pushing. So we did our study using community births, meaning births that took place at home with a midwife or in a birth center with a midwife because water birth is much more common in those settings. We ended up with a sample size where we had more than 17,000 water births and a matched sample of 17,000 land births or non-water births. The other issue that we needed to address methodologically is the idea of confounding and that’s an epidemiology term that basically means the kinds of people who choose water births are different than the kinds of people who don’t. So similarly, like the kinds of people who use sunscreen are different than the kinds of people who don’t. And if you don’t account for these differences in your analysis, you would get the wrong answer. So for instance, if you were looking at New York versus Florida, you would find that people die a lot more often in Florida, but that has nothing to do with it being Florida. It’s just that people who live in Florida tend to be older. So that’s confounding by age, right? The thing driving the death is the age of the citizens and not where they’re living. So a similar thing in this, the kinds of people who choose water birth are really different than the kinds of people who don’t. And we had to account for all of those confounders in our analysis. We used a method called propensity score matching, which allowed us to adjust simultaneously for more than 80 confounders and the most any previous paper has been able to adjust for are five or six confounders. So we’re pretty confident in these methods that we’ve got the best look at this question possible.

Miller: What do you find to be the most important confounders? The shared characteristics that were going to be the most problematic in terms of getting meaningful data?

Bovbjerg: That is not something that our analysis answered. We just adjusted for all the ones that might be confounders.

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Miller: What I guess I’m wondering, what are examples of some of the bits of noise you had to get rid of to get meaningful data?

Bovbjerg: We adjusted for all kinds of maternal demographics like age and race ethnicity and where the mom lives and whether she’s married or not, whether she is Medicaid eligible or not. All kinds of maternal demographics, and then we also adjusted for the mom’s health history, so whether she has asthma, whether she has heart disease, right? And then we also adjusted for pregnancy characteristics, like how long the pregnancy was when she had her baby? Did she have the baby on the due date? Or was it a week early? A week late? Were there any complications during the pregnancy? And then we also adjusted for various labor related variables. So these groups, the water birth and the non-water birth groups were matched on how long the labor was and whether the midwife ever thought the mom’s blood pressure was getting a little too high or all kinds of stuff about the labor as well.

Miller: I’m wondering, even if you separate out the dozens and dozens, actually, you said 80 or more confounding variables. Can you separate out the potential benefits of water births themselves from the benefit of being in the kinds of places that are open to them in the first place that are, that want to center the experiences of pregnant people as opposed to the needs and the desires of a health care system. Can you separate that out?

Bovbjerg: Our comparison group, the land births, the non-water births, was also happening with midwives in homes and birth centers. And so I think you’re absolutely right that where you give birth matters a lot, but I think we did a pretty good job of adjusting for that. Missy, do you have anything to add?

Cheyney: Yeah, I’ll add to that. I think what you’re asking us is a very important question if we think about it in this way and that is, are the findings that in this case are completely encased in birth location, right, they’re only happening at home or in a birth center? Are they actually translatable to the hospital? In the United States, 1.5% of people give birth outside of the hospital. So the vast majority of births are actually occurring in the hospital. And so this is a very important question to ask. Are they translatable? So the first step is we wanted to get the most reliable results possible based on the data set we had access to. But once you think you understand what you’re finding and in our case, that’s that water birth appears to confer risks and has relatively minimal risks that the provider needs to take into consideration. The next thing we have to ask ourselves is this translatable into the hospital setting? We spent a lot of time reflecting on that question. I can see a couple of things about, sort of our preliminary thinking on that. And what is one of the findings we had is that cord avulsion, so that’s when the cord tears or snaps as the baby’s coming up out of the water. So you can imagine as a baby’s being born under the water, there’s some impetus to bring the baby up as quickly as possible to the surface to take that first breath and your visibility may be obscured by some blood or fluids in the water. And so there’s a slightly higher increase in the number of cord avulsions that happen in the water. And that’s the tune of 20 extra core avulsions out of 10,000 births. So small but statistically significant. And so it’s important to think, midwives and physicians, wherever they’re working, should have the skill set to be able to manage those cord avulsions. So that’s an example, we would say to all providers, regardless of where you’re working, be cautious and look very carefully at the cord. Keep eyes on and make sure that you haven’t got a tear that hasn’t been diagnosed, for example.

Miller: So that is one risk that was more likely in water births. But you found that overall water births lead to better outcomes than non-water births, after you’ve controlled for all these different variables. What are the ways in which the outcomes were actually better?

Bovbjerg: So for the mom, I’m gonna keep using Missy’s example of 10,000. So for every 10,000 water births, there are six more postpartum infections in the water birth group, but those are mild and don’t lead to hospitalization as far as we can tell. So six more infections in the water birth group. But at the same time from those 10,000 women who birth in water, there are 60 fewer postpartum hemorrhages, 28 fewer postpartum hospitalizations for the mom and eight fewer severe perineal lacerations. And then for the kids, as Missy already said, there are, we expect 20 more umbilical cord snaps in the water birth group, but 12 fewer cases of respiratory distress syndrome, 20 fewer hospitalizations for the baby and no difference in neonatal death rate.

Miller: Melissa Cheney, I’m not sure if this research got into the why here, but as a midwife and a professor of medical anthropology, I’m wondering if you have an answer to it. Why is it that water births lead to better outcomes for healthy births?

Cheyney: That’s a great question. And one thing that’s really important to elevate about this study is that we now know that it isn’t just that the healthier people are in the water. Right? So that’s one concern with previous water births. When you think about the selection bias of who actually makes it into the water, you could see that water birth looks safe simply because the healthiest, low risk people are allowed to give birth in water. And so what’s really important about this study is it shows that that is not the only thing going on. How could water be conferring benefit? One of the really important things that we think about is something called the fear-pain-tension cycle. And you can imagine that when you have a headache or you’re in pain, it’s a very normal response to be fearful or stressful. Many people use warm water immersion to help relax, breathe into the experience of giving birth, which of course can be very intense. And so we think that there’s something to do with that breaking of the fear-pain-tension cycle that may have to do with it, may help the person to relax and to be able to better manage it. The other thing is that when you don’t have water birth as an option, we have to remember that part of why we wanted to do this study is that the other options people have for pain management in our country and that’s predominantly epidural anesthesia. That is not without risk. So we can understand why having the opportunity to give birth in a way that’s less disruptive, that allows normal physiologic births, birth that occurs under the power of the person’s own body to occur in a way where it’s not intervened upon could produce better outcomes. Marit and I were talking about this this morning and we wonder how much being in the water also just allows the person more space to give birth without being bothered. Often as providers we’re wanting to take heart tones and it’s important that heart tones are still taken in the water in the community setting, heart tones are monitored with a Doppler that is waterproof that allows us to engage in intermittent fetal monitoring but we’re also less likely to be asking the person to move or change positions. It’s also more difficult to do a vaginal exam in the water. And so perhaps it’s that we’re disrupting the normal hormonal processes of labor to a lesser degree when the person has sort of that barrier of water between themselves and the care provider.

Miller: Melissa Cheyney, if you are, the point of this was to show the world in a sense, or show American hospitals and doctors and midwives about the safety of water births, what do you hope hospitals will take from this research and do as a result? And I should say we have about a minute and a half left.

Cheyney: Okay, I would say that what I think this shows us is that water birth is safer than what people have assumed. So it’s important to remember that our own individual sample sizes if we’ve had a bad outcome or a baby that struggled to breathe following a water birth, it’s really important to ask: did the water do that or is there some other factor in this care that was playing a role? And these large studies allow us to sort of transcend our own personal experience and be driven more by the data. And then for proponents of water birth, I think our study also shows that it’s not as benign as we once thought. There are things to look out for. It’s important to make sure that we have eyes on the cord, as I mentioned, and also to be looking really closely, intervening early in any signs of a uterine infection following a water birth or any birth for that matter.

Miller: Melissa Cheyney and Marit Bovbjerg, thanks very much for joining us today.

Bovbjerg: Thanks for having us.

Cheyney: Yes, thanks so much.

Miller: Melissa Cheyney is a licensed midwife, has been for 20 years, currently on leave as a professor of medical anthropology at Oregon State University. Marit Bovbjerg is an assistant professor of epidemiology at OSU in the College of Public Health and Human Sciences.

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