On shouting, "SEED MY BABY WITH MY VAGINAL MICROBES!"

Co-authored by Emily Pereira, Anthropology major, University of Rhode Island

When I was pregnant, the human microbiome was hot. And news about the microbiomes of newborns was even hotter, at least to my eyes and ears because I was on the verge of having one.

This was in 2014. Studies were starting to find that babies born via c-section have different microbiomes than babies born vaginally. These findings were being interpretively linked to health problems down the road. 

Here’s a write-up of one study of a few 4-month-olds that I came across while pregnant: “Infant gut microbiota influenced by cesarean section and breastfeeding practices; may impact long-term health”

And today studies continue to pop-up that find differences in baby microbial composition and then suggest those differences may be linked to future health problems. For example, here’s a recent one from 2016 in JAMA Pediatrics: 

“CONCLUSIONS AND RELEVANCE The infant intestinal microbiome at approximately 6 weeks of age is significantly associated with both delivery mode and feeding method, and the supplementation of breast milk feeding with formula is associated with a microbiome composition that resembles that of infants who are exclusively formula fed. These results may inform feeding choices and shed light on the mechanisms behind the lifelong health consequences of delivery and infant feeding modalities.”

These discoveries about c-sections seem important because microbes are now famous for being linked to all kinds of health troubles. 

According to the American Microbiome Institute... 

“studies are finding that our bacteria (or lack thereof) can be linked to or associated with: obesity, malnutrition, heart disease, diabetes, celiac disease, eczema, asthma, multiple sclerosis, colitis, some cancers, and even autism.”

And of course many of those same things have been epidemiologically traced back to birth by c-section. Here’sa report on one study, “published in the British Medical Journal, [that] found that newborns delivered by C-section are more likely to develop obesity, asthma, and type 1 diabetes when they get older.”

Anotherfound that, “people born by C-section, more often suffer from chronic disorders such as asthma, rheumatism, allergies, bowel disorders, and leukaemia than people born naturally."

One can’t help but assume it’s all connected. If microbes are to blame for this list of problems and if c-sections are too and if c-sections are causing babies to have different microbiomes, then the following conclusion seems like a no-brainer: we need to be wiping c-sected babies with their mother’s vaginal juices.

So although I did basically nothing to prepare for a c-section (d’oh!), I imagined that if my childbirth came to surgery, that it would be really easy to avoid the risks to my baby's health by simply wiping him down with something soaked in my lady fluids.

I had even caught wind of a trial of this procedure, written-up somewhere, and so I mentioned it to my OB at a prenatal visit. She said she’d heard of it and that there was a term for it but the term escaped her. The idea excited her, but it wasn’t even remotely close to being part of regular clinical practice yet. Remember, this was summer 2014. Sensing it was too soon and out of reach, I changed the subject of conversation. Yet, I continued to believe that someone would just help me out with the whole vaginal swabbing thing if need be. It seemed simple enough. No biggie.

At the time, I didn’t Google around for tips or instructions so I don’t know what the Internet was offering up to would-be mothers/vaginal-microbe believers like me. But today it’s quite easy to find encouragement to D-I-Y transform your kid’s c-sected microbiome into a naturally-born one.

Here, let Mama Seeds explain:

“In the event of a c-section, be proactive. Mamas, we know this recommendation is not without its “icky-factor," but WOW it makes perfect sense when you think about it, and some believe it will be a standard recommendation in the future. Here goes: if your baby is born via c-section, consider taking a swab of your vaginal secretions and rubbing it on your baby’s skin and in her/his mouth. I know, ick. But when babies traverse the birth canal, they are coated in and swallowing those secretions/bacteria in a health-promoting way, so all you’re doing is mimicking that exposure. Don’t be afraid to ask your midwife or OB to help you collect the vaginal swabs—or do it yourself, if you’re comfortable. You have all the available evidence on your side.” - Michelle Bennett, MD is a full-time pediatrician, a Fellow of the American Academy of Pediatrics, a mother of two, and a founder of Mama Seeds.

Like I said, I didn’t have Mama Seeds. But I didn’t need Mama Seeds. While I was being wheeled into emergency cesarean surgery, I still shouted “SEED MY BABY WITH MY VAGINAL MICROBES!”

The reaction from the hospital staff? There was no reaction and, surprise surprise, there was no artificial seeding of my baby’s microbiome.

And that’s good. That’s how it should have gone down because my request was not based on scientific thinking. I hope you'll forgive me. I was pregnant. I wasn’t myself.

Slowly I’m becoming myself again, though, and thanks to a keen student, Emma Pereira, this post’s co-author, I’ve learned quite a bit about the science behind whether I should have seeded my newborn with my vaginal microbes. And the answer to anyone who’s wondering is a resounding NO. At least for now.

Here’s why.

1.   We don’t know if it’s necessary. Despite the increasing numbers of studies, no one to our knowledge has looked longitudinally at the microbiomes of humans born via c-section to find out if the changes detected (in very small samples) early on in these studies actually last, let alone if they can be causally linked to differences in health. It seems like the money and the technology is there to identify (via genetic sequencing) myriad microbial species, but the time and energy just isn’t there to do much else. So, although there is a growing literature, the dots aren’t connected yet. A graphic may help explain what we've learned: 

2.  You could actually harm your baby. Because there is currently no known good to come of seeding one’s c-sected baby with one’s vaginal microbes, there can only be bad. Yes, authors of this studypublished recently in Nature Medicine took a bunch of gauze that had been sitting in the mother’s vagina for an hour and swabbed 4 babies for a duration of about 15 seconds right after their birth by c-section and then found a significant difference in their microbiome at 30 days-old compared to babies who weren’t treated.  The microbiome wasn’t identical to vaginally born babies, but at least it wasn’t identical to those poor c-sected controls who didn’t get swabbed, right? Well, maybe wrong. First, please revisit number 1. And, second, maybe causing a baby to have a c-sected microbiome is not worse than seeding a baby with genital herpes, which is a very real possibility in practice, outside of these early, highly controlled pilot studies. As reported in Should C-section babies get wiped down with vagina microbes?, “the procedure could unknowingly expose newborns to dangerous bugs, pathogens that babies born by C-section usually avoid. Group B streptococcus, which is carried by about 30 percent of women, can trigger meningitis and fatal septicemia... Herpes simplex virus can lead to death and disability in newborns. And chlamydia and gonorrhea can cause severe eye infections.”

So, again, as of right now, there is no reason to seed one's c-sected baby with one's vaginal microbes. And there are very good reasons not to! 

We think that the temptation to blame the rise of numerous complex health problems to something as simple (and easily knowable) as the way we’re born is similar to the temptation to reduce these very same complexities to what’s coded in the genome. For some people, maybe even many, it may turn out to be this simple! But we’re far from knowing whether that’s true. 

Spare your baby from meddling with his microbes until the evidence is there. 

When evolutionary-minded medicine gets it (possibly) wrong about childbirth interventions

No one is saying that medicine isn't brilliant and hasn't saved lives. But it does intervene more than necessary when it comes to pregnancy and childbirth.

Part of that unnecessary intervention is driven by lack of experience. Part is an economically-driven disrespect for time. (Give childbirth some motherlovin' time.) Another part, related very much to experience, is how difficult it is to decide when intervention is and isn't necessary, especially when things are heating up. But another part of the trouble actually lies in the evolutionary perspective. Unfortunately it's not all rainbows and unicorns when M.D.s embrace evolution. Instead, evolutionary thinking is biasing some medical professionals into believing that, for example, birth by surgical caesarean is an "evolutionary imperative."

Here's one recent example in The American Journal of Obstetrics & Gynecology of how the evolutionary perspective is (mis)guiding arguments for increased medical intervention in childbirth.

link to paper

It's a fairly straight-forward study of over 22,000 birth records at a hospital in Jerusalem. The authors ask whether birth weight (BW) or head circumference (HC) is more of a driver of childbirth interventions (instrumental delivery and unplanned caesareans) than the other. Of course, the focus is on the biggest babies with the biggest heads causing all the trouble, so the authors narrow the data down to the 95th percentile for both. Presumably they're asking this question about BW and HC because both can be estimated with prenatal screening. So there's the hope of improving delivery outcomes here. And, of course, the reason they ask whether head size or body mass is more of a problem is because of evolution. They anticipate that they'll discover that heads are a bigger problem than bodies because of the well-known "obstetrical dilemma" (OD) hypothesis in anthropology.

OD thinking goes like this: Big heads and small birth canals are adaptive for our species' cognition and locomotion, respectively, but the two traits cause a problem at birth, which is not only difficult but results in our species' peculiar brand of useless babies. (But see and see.)

So, since we're on the OD train, it's no surprise when we read how the authors demonstrate and, thus, conclude that indeed HC (head circumference) is more strongly associated with childbirth interventions than BW (birth weight), at least when we're up in the 95th percentile of BW and HC. Okay.

They use this finding to advocate for prenatal estimation of head size to prepare for any difficulties a mother and her fetus may be facing soon. Okay.

Sounds good. Sounds really good if you support healthy moms and babies. But it also sounds really good if you already see these risks to childbirth through the lens of the "obstetrical dilemma" with that OD thinking helping you to support "the evolutionary imperative" of the c-section. Okay.

Too many "Okays" you're thinking? You're right. There's a catch.

When you dig into the paper you see that "large HC" heads are usually about an inch (~ 2.5 cm) greater in circumference than "normal HC" ones. (Nevermind that we chopped up a continuum of quantitative variation to put heads in arbitrary categories for statistical analysis.) And when you calculate the head diameter based on the head circumference, there is less than 1 cm difference between "large" and "normal" neonatal heads in diameter. That doesn't seem like a whole lot considering how women's bony pelvic dimensions can vary more than that.  Still, these data suggest that the difference between a  relatively low risk of having a c-section and a relatively high risk of having a c-section amounts to less than a centimeter in fetal head diameter. And maybe it does. Nobody's saying that big heads aren't a major problem sometimes! But maybe there's something else to consider that the paper absolutely didn't.

Neonatal heads get squeezed and molded into interesting shapes in the birth canal.

The data say that normal HC babies get born vaginally more often than large HC ones. But this is based on the head measures of babies who are already born! If we're pitting head circumference (HC) of babies plucked from the uterus against the HC of babies who've been through hello! then of course the vaginally delivered ones could have smaller HCs.

C-sected babies tend to have rounder heads than the ones squeezed by the birth canal. It's impossible to know but I'm fairly confident about this, at least for a subsample of a population: Birth the same baby from the same mother both ways, vaginally and surgically, and its head after c-section will have a larger HC than its squeezed conehead will after natural birth.

Measuring newborn head circumference (HC). source

When we're talking about roughly 2.5 cm difference in circumference or less than 1 cm difference in diameter, then I'd say it's possible that neonatal cranial plasticity is mucking up these data; we're sending c-sected babies over into the "large HC" part of the story just because they were c-sected in the first place. So without accounting for this phenomenon, the claim that large head circumference is more of a cause of birth intervention, of unplanned c-sections, than large body mass isn't as believable.

If these thoughts about neonatal cranial molding are worthwhile, then here we have a seemingly useful and very high-profile professional study, grounded in the popular but deeply flawed obstetrical dilemma hypothesis, that is arguing for medical intervention in childbirth based solely on the difference in head size measures induced by those very medical interventions. 

The circle of life!

Why is the human vagina so big?

We are obsessed with penis and testicle size. Yet, we can barely say "vagina" and when we do we're usually talking about the vulva.

Everyone's come across some article somewhere on-line that is thrilled to share how big human penises really are, for primates, and to explain why they evolved to be so big. It's not really the length, but the girth. Alan Dixson is your go-to on this. He's conservative in his assessment of the literature on penis size and even he concedes that human penis "circumference is unusual when compared to the penes of other hominoids (apes)" (p. 65 in Sexual Selection and the Origins of Human Mating Systems).

A favorite explanation for the big phallus is female mate choice, that females selectively make babies with males who have larger and, presumably, more pleasurable semen delivery devices. This is backed up by studies. When life size projections of naked men are shown to female subjects, they say they find the ones with bigger ones to be more attractive. [This is exactly how mate choice works where I live, how about you?]

Other explanations include male competition. If you can deliver your package to the front yard but the other guy can deliver to the front door, his is more likely to be carried inside the house first. Or, if he can steal away what you just delivered, then, again, his package has yours beat. Thanks to his big penis he's more likely to pass on his winning penis genes than you are to pass on your loser penis genes. Loser.

All this is just terribly fun to write about and I'm not even going nuts (gah) like they do. And they do. They really do. And all over the Internet they do: "Evolution of human penis" gets 53,000 hits just on scholar.google alone, and about 832,000 on Google.

But doesn't it make sense that for a penis to be somewhat useful it has to be somewhat correlated to vagina size?

I'm talking about all penises in the universe and all vaginas too. Sure there's variation, but a penis can't be too wide. It helps to be long, probably, but it can't be too long.

So neither pleasure nor psychology need matter at all, just function associated with some sort of fit. Pleasure and psychology are never invoked to explain penis morphology in other animals. If anything, it's the cornucopia of horrifying, not pleasing, animal penises that begs for evolutionary explanations.

Wouldn't you explain the size and shape of the key by the size and shape of the lock? So wouldn't it be a little more scientifically sound to hypothesize that the human penis is sized and shaped like that because it fits well into the human vagina?

Sure, it gets chicken-and-eggy or turtles-all-the-way-downy, but c'mon. Isn't it a bit obvious that the privates that fit inside the other privates are probably correlated? You'd think that even the people who have never had intercourse would default to this explanation for the evolution of the human penis.

Figure 2. Examples of genital covariation in waterfowl.

(A) Harlequin duck (Histrionicus histrionicus) and (B) African goose (Anser cygnoides), two species with a short phallus and no forced copulations, in which females have simple vaginas as in Fig 1a. (C) Long-tailed duck (Clangula hyemalis), and (D) MallardAnas platyrhynchos two species with a long phallus and high levels of forced copulations, in which females have very elaborate vaginas (size bars = 2 cm). ] = Phallus, * = Testis, ★ = Muscular base of the male phallus, ▹ = upper and lower limits of the vagina.

doi:10.1371/journal.pone.0000418.g002

But we're rarely, if ever, told that human penises are relatively girthy because human vaginas are. It's always about male competition or female preference.

Sure, we may be a little weird compared to our close relatives for not having a baculum (penis bone), and maybe that's the sort of thing you want to explain for whatever reason, but does human penis size and shape need a uniquely human story?

Assuming it's correlated to the vagina like it probably is in many other species,* then no it doesn't... unless the size and shape of the human vagina has an exceptional story.

Does it? We wouldn't know. There are zero (look!) articles titled "Why is the human vagina so big?"

Until right now.

Here we go. If we were going to answer it the same way we've long explained the human penis, and other animal penis shapes, then we've got a few ideas...

Because walking upright made the vagina conspicuous and males thought a bigger vagina was better. Because big vaginas outcompete small ones at catching sperm. Because of male pleasure from coitus with a big vagina. Because of heat dissipation or thermoregulation. Because of a tradeoff with brain size.

And of course, we'd need to demonstrate that the human vagina is in fact larger, relative to body size, than the vaginas of other primates. Regardless, a sound answer to the question of vagina size and shape focuses on childbirth, wouldn't you say? She's got to be big enough to push out a baby and, for humans, it's a great big baby. 

So if there's an exceptionally human story for the great big human penis, that exceptional story originates not in a woman's orgasms, not in her pornographic thoughts or her lustful eyes, but in her decidedly unsexy "birth canal."

And I dug up a nice little note to explain this to us all written by Dr. Bowman, a gynecologist, back in 2008 for the Archives of Sexual Behavior

That note is magnificent. It starts out giving the only vagina-size-based, not to mention childbirth-based, explanation for human penises that I can find in the literature (which is thankfully cited by Dixson in his book mentioned above). But it still manages to bring the explanation beyond the vagina and onto another proud triumph: "In sum, man’s larger penis is a consequence of his larger brain."

After you clean up the coffee you just spat onto your computer screen, you can read it all for yourself up there in the figure.

Guess who didn't read it? That study in PNAS, mentioned above, that showed women naked penises, got a high attractive score for the big ones, and thinks that's evidence for mate choice now, today, let alone back when (I'm going to speculate that) women had a tiny bit less of it.

Point is, the literature rages on with the special explanations for the big penis with nary a big vagina in sight.

But you heard it here, at least.

Childbirth is why the human vagina is so big and, consequently, why the male penis is so big. It's pretty straightforward. Yet we're still left scratching our heads as to why the penis question endures.

Is evolutionary science averse to big vaginas?

Does nobody love a big vagina?

Because that's just ridiculous. Everybody came from one.



*Unfortunately a few scholar.google searches led me to find no cross-species comparisons of mammalian vagina lengths or any vaginal measures. It may be out there, but I haven' t found it. I found some measures for bitches... DOGS! And some heifers... COWS! So I've got to compile some data if I'm to do this properly. Baby size might be a way to do this.

**UPDATE. p. 73 in Dixson has Figure 4.3 with nine primate species' penile and vaginal lengths plotted. Thanks Patrick C for reminding me where I'd seen something like this and where to point readers!