Confounding Factors and Researcher Bias

I recently read an article which bothered me:

Improved Outcomes For Newborns And Mothers With New Method Of Managing Risk In Pregnancy

Sounds good, doesn’t it? Anything that helps improve outcomes for both mothers and babies is good, right? What is this “new method of managing risk in pregnancy”? It’s called AMOR-IPAT, which stands for “Active Management of Risk in Pregnancy at Term.” (Here is the link to the published study, from the Annals of Family Medicine.) Basically, women in the study were randomized into the “control” group, which was managed with standard care, and the “exposed” group, which was looked at closely to see if there were any risks for big babies or aging placenta. Each of these is associated with a higher C-section rate, ostensibly because big babies have a harder time fitting through the mother’s pelvis, and aging placentas have a harder time supporting the baby through labor, leading to fetal distress. If these risks were found, then the woman was induced “preventively” — the more numerous or “severe” the risks, the earlier she was induced. While more women in the “exposed” group were induced, the rate of C-sections was lower. Fewer C-sections is good, so what’s the problem?

Quite a bit, actually.

First off, this study, like so many before it, compares two different interventions or methods of intervention, rather than an intervention vs. non-intervention. For instance, this study looks at two different styles of inductions, rather than comparing inducing vs. letting nature take its course. This leaves unanswered the question of, “What would have happened had these women not been induced at all?” Perhaps these so-called “aging placentas” would have been still perfectly adequate for a normal labor at 41 weeks or more, but not for an abnormal, artificially induced or augmented labor. Many studies conclude that inductions increase the C-section rate, so why does this study alone find that these doctors can induce, but have a lower C-section rate? Is it really because AMOR-IPAT is so good? Not according to this rebuttal editorial, also published in the Annals of Family Medicine, nor according to Henci Goer, who wrote this critique.

Both articles are excellent, and well worth reading. But I want to bring out a few points and talk about them.

The rebuttal editorial, “Association, not Causation: What is the Intervention?” mentions the distinct possibility of enthusiastic supporters being “less careful” in applying the AMOR-IPAT criteria. We’ve seen this happen in the “Active Management of Labor” that began in Dublin. Researchers there were able to achieve a high rate of spontaneous vaginal birth with a low rate of pain medication, and to force the women to accomplish birth within 12 hours (or at least to be fully dilated within 12 hours). The doctors concluded that women could forgo pain medication if they were assured that contractions would only last for 12 hours. It was unstated whether or not the women actually had any choice or input in the matter. Soon, “active management of labor” spread throughout the West, in hopes of repeating the results of the Dublin experiment, but it did not happen. Why? The enthusiastic supporters of the Dublin research findings left out two tiny little details — first, laboring women were not admitted until active labor (which was defined by a rigid set of protocols, and is not always insisted upon elsewhere), and more importantly, women in Dublin were constantly attended one-on-one by a midwife.

Female support at birth has been consistently shown to reduce the need for labor interventions, and also to shorten labor. In fact, one study I read of (in a book, several years ago), assigned a woman to sit in the corner of the labor room, but not actually interact with the laboring woman. These laboring women had shorter labors than the controls, who did not have a woman in the room — even though the stranger said and did nothing! So you can imagine what effect a knowledgeable midwife might have on a woman’s labor. You’ll often see active management of labor in force throughout American hospitals, especially dosages of Pitocin based on frequency of contractions, a desire for birth within 12 hours from admittance; but what you will not see is constant female attendance, unless the woman brings along a family member or friend, or hires a doula. Something like this could easily happen with this AMOR-IPAT criteria, because there are confounding factors which the researchers do not even recognize, simply because the researchers themselves were severely biased.

You can read the two critiques I’ve already linked to for all of the problems the critics noted, but the main ones I wish to speak of are the following: 1) the doctors involved in the study practice more like midwives than they do like obstetricians. The first critic put it this way: these doctors “practice an intimate and engaged style of care that is not representative of usual care.” 2) Four of the doctors in the study group were all family practitioners (who already have a low C-section rate) and one doctor was an OB; six of the care providers in the control group were OBs (who typically have higher C-section rates), while there were 3 FPs and 2 midwives (who typically have lower C-section rates). Henci Goer pointed out that women attended by FPs, whether they were in the study or the control group, had similar C-section rates. 3) The lead author is a member of the study group, which in itself lends to bias. Also, it is likely that the doctors in the “study” group had a self-fulfilling prophecy. Because they “knew” they had induced a woman before her baby got “too big” or before her placenta got “too old,” they were less likely to call for a C-section for cephalopelvic disproportion or fetal distress. After all, “the baby can’t be too big, because we’ve induced before it got too big, so let’s give her more time to labor.” See what I mean?


One Response

  1. As the main author of the study in question, I have a few comments.
    1) You were on a role when you sounded like you might consider supporting AMOR-IPAT. Why the sudden pull back? Is there any other method of care that is trying to lower the US cesarean delivery rate?
    2) Have you read the “editor’s choice” article in the May 2008 edition of the American Journal of Ob/Gyn. This article reports with use of AMOR-IPAT in a randomized controlled setting. Although the study was not large enough to fully assess AMOR-IPAT’s impact on C/S rates (c/s rates were numerically lower in the AMOR-IAPT group), the study did show lower NICU admission rates, higher uncomplicated vaginal delivery rates and a lower adverse outcomes index (AOI).
    3) There is ample evidence that complications with delivery are fewest if labor starts spontaneously at around 39 weeks gestation. Therefore isn’t it at least theoretically possible that induction of labor at that time might improve birth outcomes?
    4) How much evidence would you need to see to be convinced that AMOR-IPAT improves birth outcomes? I ask that because there are now three studies that strongly support its use, and three others that will be published later this year.

    Throwing sticks and stones at AMOR-IPAT is ok, if you are sure that preventive labor induction is bad (mind you there is very little good evidence that this is the case in the medical literature), but for goodness sake get to work and do some research comparing the current standard of care to something that you think is better.

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