Does cesarean birth put a baby at increased risk for obesity in the future? Seems a little far-fetched at first glance, but Dr. Susanna Huh and her Harvard colleagues just published a study that makes the link a bit more “near-fetched.” (The study itself is available here.)
Huh’s team found that children born by cesarean section were twice as likely to be obese at 3 years of age than were those born vaginally. This relationship held up even when factors like the mother’s weight, ethnicity, age and how many babies she’d already had were taken into account. Interestingly, it didn’t make a difference whether the cesarean was performed before or after labor started.
The study wasn’t designed to look at the reasons for the increased risk in obesity, but the Harvard team suggested several possibilities:
The first is the alteration of the gut microbiota–the sum total of all the bacteria found in the human bowel–caused by a cesarean birth. (More detail on that here and here.) This alteration can lead to low-level inflammation in the bowel which is associated with obesity.
The second possibility is that cesarean birth is just a stand-in for something else that’s happening at the same time. In this case, Huh and colleagues wonder about all the antibiotics given to women who are having cesareans. Antibiotics are known to alter the gut microbiota, but research results are mixed as to whether this is a lasting effect.
Finally, it’s possible (though unlikely) that all of this has nothing to do with the gut microbiota. There are hormones and other factors related to inflammation that surge in a mother’s bloodstream (and her baby’s) during labor, and these, obviously, are missing if a mother undergoes a cesarean before she starts labor. The lack of maternal stress response during labor could adversely impact the development of the newborn immune system, leading to the inflammation associated with obesity.
My best guess: it’s a big moosh of all of the above, plus other factors no one has even dreamed of yet. In the meantime, the issue of increased obesity risk is one more thing physicians and pregnant women should consider before deciding on how a baby is to be born.
It’s a complicated matter, this business of hatching healthy humans…
The rise and fall of VBACs
A new study by Eugene DeClercq and Frances MacDorman–my favorite epidemiologists–looks at trends in home vaginal birth after cesarean (home VBAC) from 1990-2008. The results are interesting, if not surprising, given the trends in American maternity care as a whole.
Basically, Declercq et al found that home VBACs in the U.S., while still rare events, have been increasing–most recently from 664 in 2003 to 1000 in 2008. VBACs accounted for less than 1% of home births in 1996, but are now 4% of total home births. Meanwhile hospital VBACs have decreased from 3% of total hospital births in 1996 to 1% in 2008.
VBACs underwent a steep decline in the late 1990s after the American College of Obstetricians and Gynecologists came out strongly against VBACs being performed in hospitals that did not have 24/7 OB anesthesia services, in case of the need for an emergency c-section. For a small number of women–likely those with no local VBAC alternative–this simply drove VBACs out of the hospital and “underground” – ie, into the home setting.
The safety of home VBACs can (and will) be debated endlessly. The take-home point for me, though, is that this is one more reason to integrate home birth into the larger American maternity care system. Women can’t be forced to give birth in hospitals, and neither demonizing home birth nor overstating the advantages of hospital birth is doing anyone any good. (For examples of some especially vocal opposition to home birth, see the replies to Dr. Alice Dreger’s article in The Atlantic I cited a few days ago.)
Cesareans: No problem?
Here’s a Brazilian study that claims cesarean section isn’t a risk factor for obesity, which contradicts other studies that suggest an association between the two. Interesting finding, but this will need to be confirmed in other countries. There may be something about Brazil–cultural factors like diet, for example–that may overshadow cesarean birth’s alleged obesity risk.
Bottom line: obesity is a complex topic, and there are obviously many factors involved. Cesareans still seem likely to be a contributor, but to what degree remains to be seen.
No way to spend a childhood...
Yet another study links cesarean birth with asthma. This one involved 37,000 participants in the Norwegian Mother and Child Cohort Study, and compared cesarean- and vaginally-born children for evidence of asthma at age 3. Those born by cesarean section had an increased risk of asthma.
The authors speculate that the altered gut microbiota found in cesarean babies–the collection of bacteria that live in the bowel–may be the reason for the association. (See my posts here and here for an explanation of how and why an altered gut microbiota may be at the root of a number of later chronic illnesses.)
The study’s authors described the increased risk as “slight,” which contrasts with the “moderate” risk found by other researchers. This apparently lower risk may be due in part to the how the study was performed.
First, the researchers lumped all cesareans–both scheduled cesareans and those that followed a long labor, in which a baby may be exposed to the normal bacteria of the birth canal–rather than comparing scheduled cesareans to vaginal births. The latter comparison would give a clearer picture of childhood asthma risks from cesarean birth.
Second, the study only follows the children to 3 years of age. Many cases of asthma occur later in childhood, and a longer follow-up of these children (which is no doubt in the works) would give a clearer picture of the risks.
Studies like this one add more weight to the argument for reducing the number of cesareans currently being performed, particularly those done without any medical need. Women should be informed of the potential long-term health risks and benefits for their children when choosing how and where they want to have their babies.