Will a C-Section Leave My Baby with Fewer Helpful Antibodies?

Hi Emily. There’s been a Dutch/Scottish study that found that babies born via C-section have half the amount of protective antibodies produced after childhood vaccines than those born vaginally. Is this study good? This feels pretty significant. I was set on a C-section to give birth next time after suffering a serious tear with my first baby, but now I’m worried I’d be putting them at risk to protect my own health.
—Gabi

The study you are referring to is here. In it, researchers took data from a number of babies (either 66 or 101, depending on the vaccine) and measured their degree of antibody response to vaccination. That is: they measured the amount of antibody produced after vaccination with either the pneumococcal or meningococcal vaccines.

They found that there was variation in the concentration of antibodies across individuals based on both their mode of birth and whether they were breastfed or formula-fed. They hypothesize that this response is related to gut bacteria, since gut bacteria also vary along these dimensions.

These results are interesting, and the mechanism is plausible. However, there are two important points.

First: there is a lot of complicated variation here. The antibody response in one of the vaccines is actually lowest in babies born vaginally who are formula-fed. Taken literally, this would say you’d be better off having a C-section if you were planning to formula-feed (from an antibody standpoint). That’s unlikely to be true, so we start to wonder what else is going on. These results are not randomized, so of course there are concerns about other differences across family environments and other variables. The results are also quite statistically fragile — they are statistically significant, but not wildly so.

Second: it is very unlikely that the differences here have any practical importance. The average antibody levels in all the groups are sufficient to prevent disease. Despite the breathless headlines, it is not the case that any of these groups did not show a significant and robust antibody response.

Bottom line: this should not impact your choice of birth mode. It’s an interesting fact, possibly worthy of some follow-up as we seek to better understand the microbiome. Not worth changing behavior for.