Birth Outcomes by Birth Location: The Latest Study

The much-anticipated Planned Place of Birth study out of the UK emerged last week in the British Medical Journal.  As I complete a Biostatistics course for my Master’s of Public Health ~ Maternal & Child Health program, I have to admit:  this study, including the wealth of data contained herein, is a smorgasbord for statisticians.  But for those who may not feel naturally inclined toward margins of errors and confidence intervals, interpreting the results of such a study might feel more like a nightmare. While the blogosphere has been philosophically abuzz about this new segment of data looking at the safety of childbirth practices by location, I would like to take a look at this study from a statistics perspective.  In the coming days, we will have another review of this study submitted by evidence-based maternity care expert, medical writer, and speaker Henci Goer.

The study by the Birthplace in England Collaborative Group, Perinatal and Maternal Outcomes by Planned Place of Birth for Healthy Women in Low Risk Pregnancies, is a prospective cohort study conducted through the National Perinatal epidemiology Unit at the University of Oxford.  You may recall that a prospective cohort study is an observational, forward-looking study that follows one or several groups of subjects over a specified period of time.  No assigned interventions or treatments took place as would be typical in a clinical trial. The overall objective of this study was

"to compare perinatal outcomes, maternal outcomes, and interventions in labour by planned place of birth at the start of care in labour for women with low risk pregnancies.”

The study authors explain that this study was conducted in response to several others in recent years that aimed to examine the risks and benefits associated with childbirth, relative to location, but failed to assign study groups based on planned rather than eventual place of birth. The ultimate goal of the current study, then, was to

"compare intrapartum and early neonatal mortality and specific neonatal morbidities for births planned at home…”

…in the locales detailed below.  To me, this study feels a bit similar to a case-control study as odds ratios are used extensively in the data to determine the likelihood of certain events occurring during the observed births in relation to the birth location.  (Odds ratios are commonly computed for the data of case-controlled studies.)

This study included 64,538 women who gave birth between April 2008 and April 2010 in the UK, and were segmented (not by researchers, but previously by patient choice) into one of four categories:  homebirth, free-standing midwifery centers, “alongside” midwifery units (midwife-attended birth centers within a hospital), and in-hospital obstetrics units.  Remember:  these locations pertain to pre-labour planning and initiation of intrapartum care in terms of where the woman/couple intended to give birth.  The number of birthing women in each subgroup were as follows:

As the data was collected and assimilated, further stratification of the data took place: 1) assessing outcomes of nulliparous vs. multiparous women and 2) women who did, or did not, have a “complicating condition” at the start of care in labor.  These complicating conditions included:

prolonged rupture of membranes hypertension
amniotic fluid meconium staining    abnormal vaginal bleeding
proteinuria abnormal fetal heart rate
non-cephalic fetal presentation

Women who underwent elective cesarean sections or unplanned homebirths, as well as those who were not considered “low risk” as defined by the National Institute for Health and Clinical Excellence (NICE) guidelines, were excluded from this study.  These exclusions can be seen as helpful or hindrance, depending upon the results one is interested in.  By deleting planned cesareans, there is some difficulty in being able to completely generalize the results of the data to the whole population where elective cesareans do, of course, take place—including their inherent ratios of primary and secondary outcomes.  However, in an effort to assess outcomes ofspontaneous labor and delivery outcomes, it makes sense to exclude this data.  Excluding unplanned homebirths, on the other hand, makes perfect sense to me as most of these types of births are unattended by any sort of maternity care provider, and therefore not applicable in this study design.

Outcomes assessed were broken down into primary and secondary outcomes as follows:

Primary outcomes included*:
Intrapartum stillbirth meconium aspiration syndrome
Early neonatal deaths brachial plexus injury
Neonatal encephalopathy fractured humerus or clavicle
Secondary outcomes included*:
spontaneous vertex birth syntocin augmentation
ventouse delivery immersion in water for pain relief
forceps delivery epidural or spinal analgesia
intrapartum c-section general anesthesia
3rd or 3th degree perineal tear no active management of third stage
blood transfusion episiotomy
admission to higher level of care

*notice, outcomes such as maternal mortality, postpartum hemorrhage and postnatal mood disorders are not included here.

(To access all data tables for this study, go here.)

The summarized results from the study are as follows:
The overall “primary outcomes” incidence for the entire study population was 4.3/1000 births (95% confidence interval of 3.3/1000 – 5.5/1000)  Remember, a confidence interval tells us that we are 95% sure that the true incidence of primary outcomes in the studied population, as predicted by the study data—the “point estimates”—likely falls in the interval of 3.3-5.5/1000 births.)  The incidences for each subgroup were as follows:

And from the study, a summary of the findings, per group, are as follows:

We are also given odds ratios to go along with these figures—helping us to recognize the significance of the primary outcomes, in relation to location of birth.  In essence, an odds ratio greater than 1.0 suggests that “exposure” to a variable of interest (in this case, place of birth) isa risk factor for the outcome(s) of interest.  An odds ratio less than 1.0 suggests that exposure isprotective against the outcome(s) of interest.  An odds ratio close to 1.0 suggests no significant associations between exposure and outcome.  Knowing this, let’s look at the (adjusted) odds ratios from this birth place study:

With all these numbers hovering rather close to 1.0 (with the exception of the alongside midwifery units boasting an odds ratio of less than 1.0) we can conclude that birth place may only bear a small amount of responsibility for primary outcomes—as defined in this study—in the homebirth group; negligible effect on the obstetric unit and FMU groups; and a protective effect on the AMU group.  In fact, the study authors concluded that,

"Overall, there were no significant differences in the adjusted odds ratios of the primary outcomes for any of the non-obstetric unit settings compared with obstetric units.”

Perhaps the implications made by the adjusted odds ratios would be a bit more powerful, if the study group sizes were more equal (see numbers and percentages of groups above).  And yet, for such an impressively large study, the distribution of the study population amongst the four groups is also rather impressive, considering the distribution of birth locale in the general population, as supplied by study authors: 92% of births in the UK occur within obstetric units and just 8% outside (2.8% at home; 3% in AMUs and <2% in FMUs).

The most striking outcome that anti-homebirth writers are citing as cause for alarm are the numbers for stillbirths, as delineated in the following table:

If you just look at the crude numbers, you will conclude that babies born at home are twice as likely to die during the birth process, compared to babies born in obstetric units.  Perhaps in some places around the world, this might be a very real estimate.  But in this study, we need to remember the difference in subgroup sizes:  there were 2,866 more births in the obstetric units group than in the homebirths group, for example.  So, if we instead look at the incidence of stillbirth between the groups, we get a different picture:

Now, I’m not going to sit here and suggest that even the difference between 0.2 and 0.3 stillbirths/1000 is insignificant…it’s certainly not to the additional three the families who experienced those outcomes.  I don’t think anyone should ever make that claim from an individual perspective.  But, if looking at the data from a statistics perspective—the perspective that informs us when we are advising expectant women/couples on place of birth…or when making our own decisions about birth locale—the incidences are still very low: out of the 16,839 homebirths, the stillbirth ratio for each group was:

Some other interesting numbers that came out in the data are as follows:

The above data suggests that the differences in outcomes between first time (nulliparous) mothers and subsequent (multiparous) mothers are more favorable for women who’ve undergone childbirth previously—regardless of birth location.  The study authors summarize these findings, in terms of policy implications, this way:

“Adverse perinatal outcomes are uncommon in all settings, while interventions during labour and birth are much less common for births planned in non-obstetric unit settings. For nulliparous women, there is some evidence that planning birth at home is associated with a higher risk of an adverse perinatal outcome.”

After reading the study and the statistics, what do you think???

~ Stay tuned for more coverage of this study ~

Posted by: Kimmelin Hull, PA, LCCE, FACCE


Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Bearing Meaning Doula Collective
[...] Birth Outcomes by Birth Location: The Latest Study November 29th, 2011 by Kimmelin Hull, PA, LCCE, FACCE [...]

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Karen Joy
As a natural childbirth advocate, I find it frustrating that so many studies (and consequently, doctors' and many midwives' main motivating factor in decision-making) revolves around perinatal mortality. And even an increased incidence rate of 0.001%, comparing one statistical option with another, leads some caregivers to proclaim, "Your baby may die" -- with a tiny note of truth in it -- and successfully steer a mother toward a poor decision (such as inducing after 41 weeks). What I'm reading here, the incidence rate of PNM is SO LOW, whether it's at home or in the hospital or other places of birth. I'm a little shocked that the study's numbers for the stillbirth rate *ARE* so low. I thought for the general population (at least in the U.S.), the rate was 3 per 1000 (0.003%). This study, unless I'm reading it wrong (which is very possible) says that the actual risk is about one-tenth of that!! Of course, there are more deaths that factor into PNM than just stillbirth. Still. A stillbirth rate of about 0.0003% is, to me, exciting. Not that stillbirth is exciting. It's tragic. But, that stat shows to me that, no matter where a baby is birthed, at least stillbirth stats are SO VERY LOW that it really shouldn't factor into any decision-making at all, by anyone. I'll be very interested to see what Henci Goer has to say, too. Thank you for this post.

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Walker Karraa, MFA, MA, CD
This comment is for birth advocates, not Kimmelin. I would like to suggest we consider the rates regarding maternal mental health are significantly more demonstrative of PTB, LBW, and maternal mortality. There is higher ratio of pregnant women dying through interpersonal violence, or suicide, than those choosing a home birth, or hospital births due to eclampsia/pre-eclampsia, hemorrhage, or amniotic embolism. See my post in Nov. for citations. Secondly, this is a first world problem. How much are we doing to examine this issue, or its relevance, to women of color, women of poverty, and women who don't have the privilege of choosing. Homebirths in Chad = death. Do we ever read the Millennium Goals? When will we get it that to advocate for birth means to advocate for women in every way? Compartmentalizing where and how a woman births is positivist paradigm kool-aid with which we tear empirical science apart. I would love to see a dialogue about HOW we think about birth. And how we DON'T think about birth.

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Walker Karraa, MFA, MA, CD
The other suggestions is that we need to engage in our own research and it is time to do so. Qualitative.

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Susanna
I'm a homebirther 4 times over, but those numbers that seem to show homebirth with higher negative outcomes in almost every catagory don't make me feel very good. I know it's statistically nearly negligable, but I just feel this study will easily persuade/ reaffirm for folks that homebirth is more dangerous. I'd feel a lot better if the numbers were different. Though, I still think homebirth was the best decision for me...but my 4 positive experiences just aren't statitically significan't are they?

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
@Susanna I really appreciate your shared experiences here, and thank you for offering them. In fact, I've read several editorials over recent months that suggest it's time to give more weight to individual--often qualitative, as Walker suggests--data. Yes, there is a reason why RCTs, systematic reviews and metanalysis sit atop the level of evidence pyramid...but personal experiences are NOT insignificant: they tell the REAL stories of REAL people in REAL birth settings. Your four homebirths may not be "statistically significant" to the entire population, but they are significant to you, your family, your friends, colleagues and acquaintances who know of your success with homebirth. You said it very well when you stated,"I still think homebirth was the best decision for me..." Different birthing options will feel "right" for different people, and as long as those decisions are made based on best-evidence data and optimal guidance, then we as individuals and maternity care professionals can feel good about those decisions.

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
@Karen Joy Karen, I'm glad you raise these questions, as one critique I had of the study--which I didn't have room to do justice by in the original post--is that there are SO MANY other perinatal outcomes that weren't measured: perinatal mood disorders, short and long term breastfeeding rates, short and long term maternal morbidities, c-section scar pain, perineal pain from tears or episiotomies and...yes...maternal mortality. Why didn't this study include maternal mortality in the data? If you read closely the study design and data collection sections, you'll find that data was only collected through the fifth day, postpartum. And yet, most of us working in and around the maternity care industry (and those of us who've given birth) surely know that complications pertaining to childbirth/childbirth practices can extend out, and sometimes crop up, much longer than five days postpartum.

Birth Outcomes by Birth Location: The Latest Study

November 29, 2011 07:00 AM by Karen Joy
@Kimmelin Hull Yes, indeed, you did reference other outcomes not even considered in the study; I certainly wasn't suggesting that you, in particular, are overlooking them. And, like Susanna's experience, in reading your post about the report (or perhaps the report itself), it is so very unfortunate that people may look at the raw numbers and come to a similar uneasy conclusion about homebirth, when the value homebirth is SO MUCH MORE encompassing than "just" those stillbirth numbers. Another thing to which you refer is that, clearly, with some of the outcomes, just because a woman PLANNED to deliver at home, doesn't mean she actually did. Table 8.6 (p. 71) states that 5.6% of "home"-birthing women had synctocin/Pitocin augmentation during their labor. And 8.4% of them had EPIDURALS???? Clearly, a fair portion of those planned home births did not end up being actual home births, and that in itself skews the numbers, making nearly the whole study pretty much pointless. What you PLAN on and what you DO are very often two different things.

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
@Karen Joy Yes, and I believe there is a chart in the supplemental data that demonstrates rates of transfer from home, or at least rates of admission to a higher level of care in the study. We all certainly know that you can only "plan" so much about childbirth and that anticipated homebirths sometimes don't work out. That being said, epidural-assisted births sometimes don't work out, too. I know more than a handful of women who had anticipated receiving epidural analgesia but experienced such a precipitous labor and birth that it just didn't happen. So, to me, to include the data on births that started out in one locale--but ended up in another--is actually appropriately representative of what sometimes happens in real life. I appreciate your additional thoughts!

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Juliana
What I would appreciate knowing is the cause of stillbirth. How many of these stillbirths, in all settings, are a caused by malpractice?

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
March of Dimes has done a lot of work in this field lately (preventing stillbirths). One of their big campaigns is to stop the practice of inductions prior to 39 completed weeks. ("Healthy Babies are Worth the Wait") You might enjoy checking out the work they've done (if not, already!)

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
Submitted by Science & Sensibility reader Jaylon VonMertens,RN: I'm an RN and homebirth midwife. In looking at the data you presented, I wonder about the incidence of stillbirth in the homebirth population. I wonder if the lower incidence in the OB group has to do with increased fetal surveillance in the 3rd trimester which homebirth clients often decline? Do they give a NNT (number needed to treat) for stillbirth for the OB group? In other words, how many women have to get intensive 3rd trimester fetal surveillance in order to prevent one stillbirth? Curious. Of course, here in the US, it will get tossed aside because they have an integrated system and we do not, to which I always reply, "Why not create an integrated system?"

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
@Kimmelin Hull Jaylon brings up an interesting point here re: NNT (number needed to treat) is a statistic that would help us understand how many interventions would be needed to prevent one stillbirth. Ok, so let's get into some more statistics: Assumptions: we're going to look at the absolute risk of stillbirth using homebirth location as the "event group" and obstetric unit birth as the "control group" Event rate of stillbirth (EER): 6/16839 = 0.0003563157 Control rate of stillbirth (CER): 3/19706 = 0.0001522379 Absolute Risk Ratio: |EER-CER| = 0.0003563157 - 0.0001522379 = 0.0002040778 Number Needed to Treat (NNT) = 1/ARR 1/0.0002040778 = 4900.092 What this tells us is that whatever "treatments" are delivered at the OB unit level to decrease the number of stillbirths, compared to the number in the homebirth setting...nearly 5,000 women would need to undergo these "treatments" in order to prevent one stillbirth in the homebirth setting. This answer presents a problem for us as we cannot pin one individual difference in treatment on the OB setting...we all know there are MANY differences between OB labor and delivery care vs. homebirth L&D care--reserving judgment on which differences constitute "good" vs. "bad" differences. We're talking about two different paradigms with multiple components within each paradigm, so we are left with an inexact answer to the question about number needed to treat.

Birth Outcomes by Birth Location: The Latest Study

November 30, 2011 07:00 AM by Sue
I have a few comments to make about this study. Firstly, there were tight exclusion criteria - so the population studies does not necessarily refelct the HB population. Secondly, there were VERY high tranfer rates, so the study din't look at the HB environment in isolation - it looked at HB with obstetric unit backup. Thirdly, their definition of "secondary outcomes" is strange - it includes both real outcomes (complications) but also access to pain relief (not generally considered to be a "complication"). What they have shown is that, no matter how much risk is eliminated before labor, the HB environment still carries a measurably increased risk of neonatal death. Of course it is (thankfully) small - but the trade-offs for that improvement in outcome does not seem too great. In this study, nearly half the women laboring in hospital had a totally intervention-free birth. This seems like the ideal compromise between "natural" process but with the best safety profile.

Birth Outcomes by Birth Location: The Latest Study

December 1, 2011 07:00 AM by Paivi Laukkanen
Sue, When they say normal births, it means in this study, that they were not induced, had no epdural or spinal, no cesarean, and no episiotomy. These women would have still had pitocin augmentation, other pharmacological drugs, and managed third stage. So, it's still far from intervention free, but I guess there's no way to know the exact truth.

Birth Outcomes by Birth Location: The Latest Study

December 1, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
Another recently submitted comment on this post: ************************************************** "Thank you for this thoughtful study guide to the data. "I wondered if the stillbirth-at-home figure may represent women with known late fetal demise who nevertheless choose to give birth at home (as I would have done had it been an option at the time, after hearing the experience of a friend who did so in similar circumstances)." ~ Katharine Hikel, MD

Birth Outcomes by Birth Location: The Latest Study

December 2, 2011 07:00 AM by Laura
What I think is interesting is to notice the outcomes that were lower with midwives or out-of-hospital birth. For example, overall outcomes for meconium aspiration syndrome were much lower in out-of-hospital birth. Why would that be? It makes me think of my mom's response to "What if..." questions about homebirth. Her theme seems to be that babies feel more comfortable at home and therefore, complications are avoided. And of course, that's not true always - babies still die at home. But maybe it has to do with the reason that the incidence of meconium aspiration syndrome is lower. I myself had meconium aspiration syndrome when I was born (in the hospital), and I did ask her once the question of what if I had been born at home. And she told me that she feels it wouldn't have happened.

Birth Outcomes by Birth Location: The Latest Study

December 2, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
@Laura In the multiparous population, yes, meconium aspiration syndrome was demonstrated the lowest incidence among all groups at 0.6/1000. But the nulliparous (first time mothers) group actually had the highest incidence of all groups at 3.3/1000. Many commentators on this study have been citing this data discrepancy--with first time mothers seeming to have more complications at home vs. other groups--as evidence that homebirth is generally "unsafe." I think we do have to be cautious in making this type of judgment in that the numbers we're talking about are quite small--even if different than each other. The idea you raise re: how an at-home birth "feels" different is an interesting one that may very well carry significance, (ask any homebirther who had a positive experience and I suspect she will concur), but also hard to "prove" in a study. But, alas, I'm not sure that every human experience must be "proven" to be considered credible. Regardless, practice bulletins and recommendations are built upon statistics...but the question remains, which statistics are being employed by which to build those recommendations?

Birth Outcomes by Birth Location: The Latest Study

December 2, 2011 07:00 AM by Science & Sensibility » Birth Outcomes by Birth Location: The Latest Study « Texas Bi
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Birth Outcomes by Birth Location: The Latest Study

December 2, 2011 07:00 AM by Karen Joy
@Kimmelin Hull Yes, intentions and eventualities do go both ways. My sister was planning on asking for an epidural as soon as she could, but had a precipitous birth: First contraction until baby's arrival was one hour, twenty minutes! I like this: "So, to me, to include the data on births that started out in one locale–but ended up in another–is actually appropriately representative of what sometimes happens in real life." That is a great point. My problem, though, is that the study is already being used extensively by those who are antagonistic toward homebirth, when the numbers aren't necessarily from those who actually HAD a homebirth.

Birth Outcomes by Birth Location: The Latest Study

December 5, 2011 07:00 AM by Kathy
30% = .3 = 3/10 or 30/100 3% = .03 = 3/100 .3% = .003 = 3/1000 .03% = .0003 = 3/10,000 .003% = .00003 = 3/100,000 Percent is "per cent" -- literally "per hundred", or dividing by 100. You have to move the decimal point two places to the left, adding zeros as necessary. Yeah, I learned that lesson really well in school, after careless errors cost me points on tests. ;-)

Birth Outcomes by Birth Location: The Latest Study

December 6, 2011 07:00 AM by Kimmelin Hull, PA, LCCE
Keeping Kathy's helpful summary up here to summarize recent conversation about the stats with MT, myself and Kathy, and to avoid detracting from the overall conversation on the study. Thanks ~

Birth Outcomes by Birth Location: The Latest Study

May 2, 2012 07:00 AM by D L Dahly
Enjoyed your take on this. Here was my own attempt:

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