Maternal Obesity from All Sides (Part 6)

June 13th, 2011 by avatar

[Editor's note:  In today's post, sixth out of our eight-part series on maternal obesity, Pamela Vireday takes a closer look at the research surrounding pregnant women of size.  To read Pam's first post, go here.  To read this series from the beginning, go here.]

Rethinking the Paradigm: An Insider’s View (Part Two)

Previously, we discussed the risks around obesity and pregnancy, and why they need to be communicated more compassionately and with a more precise sense of actual numerical risk.

Now let’s examine the research with a more critical eye.


Rethinking Research
One major problem with research on obesity and pregnancy is that it’s rarely analyzed for iatrogenic factors, which can have considerable effect. For example, how much of the increased cesarean rate in women of size is due to obesity itself, and how much is due to typical management protocols used on obese women or fears about their labors?

Many studies show that obese women are induced at higher rates than women of average size, even when they have no complications.  We know that induction (especially in first-time mothers) often increases the rate of cesareans. Yet almost no researchers connect the dots between a high rate of inductions in obese women and their increased rate of cesareans.

But are these inductions necessary?  Sometimes ─ but many are questionable.  For example, many obese women report being induced early because of the fear of a big baby getting stuck.  Obese women do have a higher rate of big babies, but most have average-sized babies (83% in one study).  Yet many doctors act as if they all will have big babies and act accordingly.

The practice of inducing early for suspected macrosomia does not improve outcome; it raises the cesarean rate and increases the risk for shoulder dystocia, the very thing doctors are trying to avoid.  A review of the issue found that “suspicion of macrosomia is not an indication for induction or for primary cesarean delivery.” Yet many providers disregard these guidelines, particularly with high-BMI women.

Just the expectation of a big baby strongly raises the rate of inductions and lowers the threshold for cesareans. In one study, the suspicion of macrosomia before labor raised the c-section rate from 16.7% to a whopping 57.1%. They found that the actual size of the baby itself had much less impact on the cesarean rate than the expectation that the baby would be big and the resulting management of labor.

Indeed, Graves 2006 found that the combination of obesity, macrosomia, nulliparity, and induction doubled the risk for cesarean section.  Wolfe 2011 found that women with a BMI of 40 or more without a previous vaginal birth and who carried a macrosomic fetus had an 80% rate of failed induction.  Clearly, the combination of suspicion of macrosomia and induction is a powerful factor driving the rate of cesareans in obese women.

Yet most macrosomic babies can be born vaginally when given the chance, and spontaneous labor is key.  Avoiding induction, encouraging mobility in labor and pushing, discouraging epidurals, and avoiding forceps/vacuum extraction might lessen the risk for shoulder dystocia in women of size.

Another iatrogenic factor in high cesarean rates in this group is the overutilization of interventions like internal fetal monitoring, pitocin augmentation, early amniotomy, and early epidurals.  Abenhaim and Benjamin 2011 showed that when interventions like pitocin use and epidurals were controlled for, the relationship between BMI and cesareans was markedly attenuated. Yes, labor progression in high-BMI women tends to be slower, but perhaps all that is needed is a tincture of patience instead of extra interventions.

They also found that doctors were far quicker to resort to cesareans in obese women, speculating that doctors fear that a heavier woman necessarily means a bigger baby that could get stuck in the birth canal.”  The authors conclude, “Because of the potential morbidities associated with Caesarean section, we must modify our management approaches to allow equal opportunity for vaginal birth for all women.”

However, many care providers now won’t even give high-BMI women a chance to labor at all, believing that vaginal birth is exceedingly unlikely and far too dangerous. Recently, the NHS in the United Kingdom conducted a study to see whether planned vaginal delivery or planned cesarean delivery was safer for super obese women (BMI >50).  An accompanying commentary admitted that it is



the frequently voiced opinion at midwifery, obstetric and anaesthetic conferences that the safest way to deliver a woman with a body mass index (BMI) over 50 kg/m2 may be by elective CS.


However, the authors found that when given the chance to labor, 70% of women with a BMI greater than 50 were able to give birth vaginally, without the “expected” increase in neonatal and postnatal complications.  This shows that very fat women can give birth vaginally if given an adequate chance, and in doing so, avoid the considerable risks associated with cesareans in obese women.

Confounding factors are not always accounted for in cesarean rate studies either. For example, doctors have tried to blame more dystocia in obese women on ineffective contractility, soft tissue dystocia or high cholesterol levels. However, Jensen 1999 found higher rates of persistent posterior babies in obese women; this is supported by anecdotal evidence that many women of size have cesareans for fetal malpositions. Since malpositions can cause longer labors, more interventions, and more cesareans, we need additional research to explore this possibility further.

Another confounding factor rarely accounted for in cesarean rate studies is the influence of menstrual cycle length and “postdates” pregnancies.  Research shows that women of size have longer menstrual cycles; perhaps this is why they have more “postdates” pregnancies.  Women whose cycles are only longer by a week or so fall into the “margin of error” in ultrasound dating and rarely have their due dates adjusted, but even a week can make a difference in how ready a woman’s body is for labor.

If these women are induced for “postdates” pregnancies when they are not truly postdates, then that may be another reason for a higher rate of failed inductions for postterm pregnancy in obese women. Perhaps the real story here is that these women’s bodies were not yet ready for labor due to longer menstrual cycles and unadjusted due dates.

There are only a few examples of iatrogenic and confounding factors that may be influencing outcomes in women of size.  Researchers must start becoming more cognizant of these and many others.


Looking For More Meaningful Research
The bottom line is that research on obesity in pregnancy needs to diversify.  Currently, the research contents itself with documenting increased complication rates and little more.  This is not without value, but its usefulness is limited.  We need to stop wringing our hands and clutching our pearls about the horrors of obesity and start doing more meaningful research.

We need more information on the cause of complications in obese women.  Remember, correlation is not causation.  Just because obesity is associated with certain complications does not mean it causes those complications.  Instead, the real problem may be an underlying metabolic or hormonal disorder (like Polycystic Ovarian Syndrome), and obesity may merely be a symptom instead of a cause.  This opens up many new possibilities for treatment, regardless of weight loss status.

Similarly, research on obesity and complications needs to ask deeper questions.  Many obese pregnant women never develop complications, yet rarely are studies done that compare the obese women with complications to those without.  Perhaps there are differences in metabolism or behavior that can explain differing outcomes, and if so, these could suggest further prevention strategies.

Recent research has shown that many obese people have multiple nutrient deficiencies, so some have speculated about the potential benefits of supplementation. For example, 400 mcg of folic acid is not protective against neural tube defects in obese women, so some obstetric organizations recommend a very high dose instead. Yet little actual research has yet been done to investigate the safety and efficacy of this possibility.

Women of size also have a much higher rate of vitamin D deficiency than other women, and vitamin D levels have been tied to higher cesarean rates, more gestational diabetes, and more hypertension. Perhaps supplementation or more sun exposure might help lower these risks.

And given the research on how high-intervention care affects outcome in obese women, it is especially important to examine the recent trend to deny high-BMI women access to low-intervention care.  Perhaps low-intervention care models actually achieve better outcomes in women of size ─ but we won’t know unless we study it.

These are only a few areas of research to explore; there are many other possibilities as well. We need to stop stumbling around in the dark with blinders on, ignoring iatrogenic and confounding factors and operating on sheer guesswork as to what will improve outcomes.  It’s time for research on this topic to stop its simplistic approach and start asking more meaningful questions.

Additional References and Links:

Subject Studies and Links
Cesarean Rate in Obese Women Chu 2007 http://www.ncbi.nlm.nih.gov/pubmed/17716296 

Vahratian 2005 http://www.ncbi.nlm.nih.gov/pubmed/15921926

Poobalan 2009 http://www.ncbi.nlm.nih.gov/pubmed/19021871

Induction and Obesity Jensen 2003 http://www.ncbi.nlm.nih.gov/pubmed/12861169 

Graves 2006 http://www.ncbi.nlm.nih.gov/pubmed/16814219

Bhattacharya 2007 http://www.biomedcentral.com/1471-2458/7/168

Michlin 2000 http://www.ncbi.nlm.nih.gov/pubmed/10892363

Pevzner 2009 http://www.ncbi.nlm.nih.gov/pubmed/19935035

Wolfe 2011 http://www.ncbi.nlm.nih.gov/pubmed/21621187

Induction and Cesareans Dunne 2009 http://www.ncbi.nlm.nih.gov/pubmed/20085677 

van Gemund 2003 http://www.ncbi.nlm.nih.gov/pubmed/14530612

Vardo 2011 http://www.ncbi.nlm.nih.gov/pubmed/21366123

Macrosomia and Obesity Bhattacharya 2007 http://www.biomedcentral.com/1471-2458/7/168 

Ehrenberg 2004 http://www.ncbi.nlm.nih.gov/pubmed/15467573

Narchi and Skinner 2010 http://www.ncbi.nlm.nih.gov/pubmed/20925609

Induction for Macrosomia, 

And Cesarean Rates

Leaphart 1997 http://www.ncbi.nlm.nih.gov/pubmed/9086425 

Melamed 2010 http://www.ncbi.nlm.nih.gov/pubmed/20103792

Parry 2000 http://www.ncbi.nlm.nih.gov/pubmed/10664942

Zamorski and Biggs 2001 http://www.ncbi.nlm.nih.gov/pubmed/11201695

Sanchez-Ramos 2002 http://www.ncbi.nlm.nih.gov/pubmed/12423867

Induction and Shoulder Dystocia Jazayeri 1999 http://www.ncbi.nlm.nih.gov/pubmed/10214826 

Combs 1993 http://www.ncbi.nlm.nih.gov/pubmed/8459954

Obesity and Menstrual Cycle Length Symons 1997 http://www.ncbi.nlm.nih.gov/pubmed/9074747 

Kato 1999 http://www.ncbi.nlm.nih.gov/pubmed/10608360

Obesity and Postdates Pregnancy Graves 2006 http://www.ncbi.nlm.nih.gov/pubmed/16814219 

Sarkar 2007 http://www.ncbi.nlm.nih.gov/pubmed/17963180

Interventions in Obese Labors Ray 2008 http://www.ncbi.nlm.nih.gov/pubmed/18569473 

Andreasen 2004 http://www.ncbi.nlm.nih.gov/pubmed/15488115

Jensen 1999 http://www.ncbi.nlm.nih.gov/pubmed/10535344

Roofthooft 2009 http://www.ncbi.nlm.nih.gov/pubmed/19412095

Soens 2008 http://www.ncbi.nlm.nih.gov/pubmed/18173431

Abenhaim 2011 http://www.ncbi.nlm.nih.gov/pubmed/21639963

More Difficult Labors/Labor Dystocia Vahratian 2004 http://www.ncbi.nlm.nih.gov/pubmed/15516383 

Walsh 2011 http://www.ncbi.nlm.nih.gov/pubmed/21158492

Arrowsmith 2011 http://www.ncbi.nlm.nih.gov/pubmed/21265999

Possible Reasons for More Labor Dystocia in Obese Women Higgins 2010 http://www.ncbi.nlm.nih.gov/pubmed/19828431 

Jie Zhang 2007 http://www.ncbi.nlm.nih.gov/pubmed/17913965

Wischnik 1992 http://www.ncbi.nlm.nih.gov/pubmed/1290280

Barau 2006 http://www.ncbi.nlm.nih.gov/pubmed/16972860

Risks of Cesareans in Obese Women Chisaka 2004 http://www.ncbi.nlm.nih.gov/pubmed/14698829 

Alanis 2010 http://www.ncbi.nlm.nih.gov/pubmed/20678746

Vricella 2010 http://www.ncbi.nlm.nih.gov/pubmed/20673866

Posted by:  Pamela Vireday, who is a childbirth educator, writer, woman of size, and mother to four children. She has been collecting the stories of women of size and writing about childbirth research for 16 years. She writes at www.plus-size-pregnancy.org and blogs at www.wellroundedmama.blogspot.com.

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  1. avatar
    June 13th, 2011 at 18:39 | #1

    kudos for such thoroughly balanced research!

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