In other words, are poor outcomes only due to "obesity" or do some poor outcomes reflect the interventive way that obese women are often managed in pregnancy and birth?
This is a particularly relevant question for the high cesarean rates found in "morbidly obese" women (BMI of 40 or more). If a high-BMI woman is perceived as ultra high-risk, and is therefore subjected to increased rates of interventions (like inductions, early epidurals, and a lower threshold for surgery), does the resulting high cesarean rate really reflect problems with obesity itself, or with the way obese women are managed?
Here are two studies of cesarean rates in women of size that demonstrate that iatrogenic (provider-caused) influences can have a very strong effect on cesarean rates, and that a high cesarean rate in morbidly obese women is NOT just about the obesity itself.
These two studies examined cesarean rates in "super obese" women (BMI of 50 or more), one from Kentucky and one from the U.K. The Kentucky study found a super-high c-section rate, and the U.K. study did not.
Yet the two studies basically were looking at very similar study groups, women with a BMI of 50 or more. If cesarean rates really are tightly tied to obesity and obesity alone, shouldn't the cesarean rates in these two studies be similar?
In the Kentucky study, women with a BMI over 50 had a whopping 56% cesarean rate. Compare that with the British study that found a 30% cesarean rate in women with a BMI over 50.
The Kentucky cesarean rate was nearly DOUBLE the rate of the British group, even though the size of the women was similar.
This strongly suggests that management of labor around the pregnancies of supersized women differed and highly influenced the resulting cesarean rate, and that it's NOT just about a woman's size, but also her care provider's management.
We can't tell for sure from these particular studies why the cesarean rates in women of size in these two places are so different, but it's a good bet that it's NOT because the uteri of British women are that much more efficient than those of Kentucky women. No, the contrast in rates is much more likely to be due to differences in care, attitudes, and interventions.
A couple of strong possibilities spring to mind.
First, midwives are the most prevalent form of care provider for most women in the U.K., whereas most women in the USA get their care from OBs. Research shows that on the whole, midwives tend to have lower cesarean rates, even when the risk profiles of patients are similar. So perhaps the cesarean rate is lower because more of the "super obese" women in the U.K. had access to midwifery care. If so, this is yet another reason to be alarmed about the move towards restricting fat women's access to lower-tech birthing alternatives and midwifery care.
Second, we don't know that much about the types of intervention, induction rates, and threshold for surgical intervention in each study. My guess is that the Kentucky study had very high induction rates (which tends to lead to higher cesarean rates), a higher rate of interventions, and a lower threshold for doing a cesarean in labor.
I would love to see more research that focuses on why there can be such different outcomes in "morbidly obese" women. We need to really shine a spotlight on differing management protocols and how they impact cesarean rates ─ and particularly so in women of size.
Interestingly, the Kentucky study notes that pitocin augmentation in labor led to lower cesarean rates in these women, although this difference did not rise to statistical significance. They speculated, therefore, that "a qualitative or quantitative deficiency in the hormonal regulation of labor exists in the morbidly obese parturient."
This is a theory that is often bandied about in obstetric research (without any supporting proof, but often accepted as gospel anyhow). Yet if this were true, why were 70% of British women able to birth vaginally? It's far too easy and convenient to blame fat women's hormones instead of looking more closely at your own management practices instead.
It's time for doctors to stop scapegoating obesity alone for high cesarean rates in women of size, and long past time for them to start examining more closely how their own biases and high-intervention protocols negatively influence outcomes in this group.
This is not an emotionally comfortable thing to study, because care providers are human and no one wants to acknowledge that their own biases and management can affect outcome so strongly. I understand that.
But if care providers are truly interested in improving outcomes in "obese" women, then this is the kind of work that MUST be done.
The contrast between these studies shows that most very fat women CAN give birth vaginally....if caregivers would just stand aside and let them. It's time to take off the blinders and see how management protocols can influence that.
Am J Perinatol. 2011 Jun 9. [Epub ahead of print] Extreme Morbid Obesity and Labor Outcome in Nulliparous Women at Term. Garabedian MJ, Williams CM, Pearce CF, Lain KY, Hansen WF. PMID: 21660900
Source: Department of Obstetrics and Gynecology, University of Kentucky, Lexington, Kentucky.
We examined the prevalence of cesarean delivery (CD) among women with morbid obesity and extreme morbid obesity. Using Kentucky birth certificate data, a cross-sectional analysis of nulliparous singleton gestations at term was performed. We examined the prevalence of CD by body mass index (BMI; in kg/m (2)) using the National Institutes of Health/World Health Organization schema and a modified schema that separates extreme morbid obesity (BMI ≥50) from morbid obesity (BMI ≥40 to less than 50). Bivariate and multivariate analyses were performed. Multivariate modeling controlled for maternal age, estimated gestational age, birth weight, diabetes, and hypertensive disorders. Overall, 83,278 deliveries were analyzed.
CD was most common among women with a prepregnancy BMI ≥50 (56.1%, 95% confidence interval 50.9 to 61.4%). Extreme morbid obesity was most strongly associated with CD (adjusted odds ratio 4.99, 95% confidence interval 4.00 to 6.22).
Labor augmentation decreased the likelihood of CD among women with extreme morbid obesity, but this failed to reach statistical significance. We speculate a qualitative or quantitative deficiency in the hormonal regulation of labor exists in the morbidly obese parturient. More research is needed to better understand the influence of morbid obesity on labor.
BJOG. 2011 Mar;118(4):480-7. Planned vaginal delivery or planned caesarean delivery in women with extreme obesity. Homer CS, Kurinczuk JJ, Spark P, Brocklehurst P, Knight M. PMID: 21244616
Source: National Perinatal Epidemiology Unit, University of Oxford, UK.
Source: National Perinatal Epidemiology Unit, University of Oxford, UK.
OBJECTIVE: To compare the outcomes of planned vaginal versus planned caesarean delivery in a cohort of extremely obese women (body mass index ≥ 50 kg/m(2)).
DESIGN: A national cohort study using the UK Obstetric Surveillance System (UKOSS).
SETTING: All hospitals with consultant-led maternity units in the UK.
POPULATION: Five hundred and ninety-one extremely obese women delivering in the UK between September 2007 and August 2008.
METHODS: Prospective cohort identification through UKOSS routine monthly mailings.
MAIN OUTCOME MEASURES: Anaesthetic, postnatal and neonatal complication rates.
RESULTS: After adjustment, there were no significant differences in anaesthetic, postnatal or neonatal complications between women with planned vaginal delivery and planned caesarean delivery, with the exception of shoulder dystocia (3% versus 0%, P = 0.019). There were no significant differences in any outcomes in the subgroup of women who had no identified medical or antenatal complications.
CONCLUSIONS: This study does not provide evidence to support a routine policy of caesarean delivery for extremely obese women on the basis of concern about higher rates of delivery complications, but does support a policy of individualised decision-making on the mode of delivery based on a thorough assessment of potential risk factors for poor delivery outcomes.