Today's guest post is written by Dr. Mark Sloan, pediatrician and author of Birth Day: A Pediatrician Explores the Science, the History and the Wonder of Childbirth. Dr. Sloan takes a look at the study released in May, 2012 examing the relationship between Cesarean deliveries and obesity in preschoolers. - SM

I don't recall learning much about childhood obesity in my early-1980s pediatric residency. This was partly due to the fact that obesity wasn't all that common-only about 7% of kids fell into that category at the time-and partly because the solution seemed obvious, and not quite worthy of medical attention. "Join a baseball team, kid," my senior resident once told an overweight boy with asthma. "And you," he said, pointing an accusatory finger at the boy's mother. "Stop buying cookies, okay?"

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One thing I did learn a lot about in residency, though, was cesarean section. The U.S. cesarean rate topped 20% for the first time, up from 6% just a decade earlier. I spent a steadily increasing amount of time in operating rooms, waiting for an obstetrician to hand me a baby.

We all thought the rise in cesareans was a good thing-think of the lives saved, the brain damage avoided, we told ourselves. If anyone had suggested cesarean birth might be creating long-term health problems for those "saved" babies, we would have scoffed. And had anyone suggested that it might lead to a lifetime of obesity, we'd have laughed them right out of the hospital.

But here we have it: The cesarean rate is now 50% higher than it was in 1980. (Hamilton BE, Martin JA, & Ventura SJ. 2011) The rate of childhood obesity has tripled. (Ogden C. & Carroll M., 2010) Is this just a coincidence?

Theories abound as to the cause of the childhood obesity epidemic. It's all those sodas and sports drinks laden with high fructose corn syrup. Or it's sugary, fatty, super-sized fast food. Or video games, the loss of Physical Education at school, bad parenting, unsafe neighborhoods, too little sleep, too much schoolwork, or all of the above. Just about any variable you can think of has been scrutinized for obesogenic potential.

And now, thanks to Dr. Susanna Huh and her research team at Harvard University, we can add cesarean section to the list of suspects.

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Huh's team studied 1,255 mother-child pairs recruited between 1999 and 2002 as part of Project Viva, a longitudinal prebirth cohort of mothers and babies in eastern Massachusetts. A trained research assistant conducted in-person visits with the mothers during pregnancy, and with mothers and babies shortly after delivery, and at 6 months and 3 years after birth. At each visit the children's length, weight and skin-fold thicknesses were assessed.

Their results: Children born by cesarean section were twice as likely to be obese at 3 years of age than those born vaginally. (Huh, SY, Rifas-Shiman, SI, Zera, CA, Edwards, JWR, Oken, E, Weiss, ST, & Gillman, MW, 2012) This relationship held up even after adjusting for factors like the mother's weight, ethnicity, age, education, and parity, and the baby's gender, gestational age, and birth weight.

The Huh study wasn't designed to look at the reasons for the increased risk of obesity associated with cesarean birth, but the Harvard team suggested several possibilities:

1. The most likely culprit is the known alteration of the gut microbiota-the sum total of all the micro-organisms found in the healthy human bowel-caused by cesarean birth. The microbiota of vaginally-born babies is populated by bacteria acquired from the birth canal and maternal rectum. In cesarean-born babies, who do not traverse the birth canal, the microbiota is dominated by bacteria from the skin and the hospital environment. In general, cesarean-born babies have an abnormal gut microbiota: too many carbohydrate-loving Firmicutes bacteria and too few obesity-preventing Bacteroidetes species, compared with the microbiota found in vaginally-born babies. This same gut microbiota profile is associated with obesity in adults; the link between the two appears to be low-level bowel inflammation triggered by the abnormal microbiota, which alters how food is absorbed from the gut and processed within the body.
2. The second possibility is that cesarean birth is just a stand-in for something else that's happening at the same time. In discussing their findings, Huh and colleagues speculate about antibiotics routinely given to women during the course of a cesarean. Antibiotics given during pregnancy may temporarily alter the newborn gut microbiota, but research results are mixed as to whether this is a significant, lasting effect.
3. It's possible that all of this has nothing to do with the gut microbiota. There are maternal and placental hormones, and immune and inflammatory factors, surging in a mother's (and baby's) bloodstream during labor. These, obviously, are missing to some extent if she never completes labor, and are largely absent if a cesarean is performed before labor starts. The lack of a normal maternal stress response to labor could adversely impact the development of the newborn immune system, theoretically leading to the gut inflammation associated with obesity.
4. Differences in mode of feeding may be involved as well. The study's cesarean babies breast-fed for a significantly shorter time than did the vaginally-born babies. Though the authors don't comment on this, early weaning is also associated with alterations of the infant gut microbiota.

My best guess: the cesarean-obesity link is likely a big mash-up of all of these, plus other factors no one has yet even dreamed of. Further research by Dr. Huh's team and many others in the coming months and years will hopefully clarify the picture.

In the meantime, the risk of future obesity is one more factor maternity care providers and their pregnant clients should weigh before deciding on how a baby will be born.

Would you be likely to share this connection between mode of delivery and childhood obesity with your students when teaching about benefits and risks of cesarean section? Do you think if more families knew about this connection, they might make different choices surrounding the labor and birth of their baby and avoid interventions likely to increase their risk of a cesarean birth. Is this information just one more thing that blames mothers for things that are out of their control? Please share your thoughts in our comment section. -SM

References

Hamilton BE, Martin JA, Ventura SJ. Births: Preliminary data for 2010. National vital statistics reports; vol 60 no 2. Hyattsville, MD: National Center for Health Statistics. 2011.

Huh, Susanna Y, Rifas-Shiman, Sheryl L, Zera, Chloe A, Edwards, Janet W Rich, Oken, Emily, Weiss, Scott T, & Gillman, Matthew W. (2012). Delivery by caesarean section and risk of obesity in preschool age children: a prospective cohort study. Archives of Disease in Childhood. doi: 10.1136/archdischild-2011-301141

Ogden Cynthia, & Carroll Margaret, U.S. Department of Health and Human Services, Centers for Disease Control and Prevention, Division of Health and Nutrition Examination Surveys (2010). Prevalence of obesity among children and adolescents: United states, trends 1963-1965 through 2007-2008. Retrieved from CDC/National Center for Health Statistics website: http://www.cdc.gov/nchs/data/hestat/obesity_child_07_08/obesity_child_07_08.htm

About Mark Sloan

Mark Sloan has been a pediatrician and a Fellow of the American Academy of Pediatrics for more than 25 years. Dr. Sloan graduated from the University of Notre Dame in 1975, received his medical degree from the University of Illinois, Chicago, in 1979, and completed his pediatric training at the University of Michigan. Since 1982 he has practiced with the Permanente Medical Group in Sacramento and Santa Rosa, California, where he was Chief of Pediatrics from 1997 to 2002. He is an Assistant Clinical Professor in the Department of Community and Family Medicine at the University of California, San Francisco. Dr. Sloan's first book, Birth Day: A Pediatrician Explores the Science, the History and the Wonder of Childbirth was published in 2009 by Ballantine Books. His writing has appeared in the Chicago Tribune, the San Francisco Chronicle, the San Francisco Examiner, and Notre Dame Magazine, among other publications. Dr. Sloan can be reached through his blog.

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