Saturday, June 18, 2011

Birth canals, craniums, and a paleoanthropological approach

Here are some of my reflections based on recent discussions with some mamas regarding natural birth and C-section rates in the US.  As we focused largely on the whole question of "pelvic disproportion", I thought I'd share a blog/article I stumbled across. The blogger was rushed into an induc/c-section before she was ready with her firstborn, but after a traumatic HBAC, she started asking the same questions I have been for years.

She posted this full article from Scientific American (2003) which simply explores the evolution of human labor and delivery culture. Hopefully the lingo won't bog you down too much (it reads like a lot of my 3rd and 4th year undergrad assignments ). Since the article is devoid of any agendas (pro-medical nor pro-natural birth), I found it refreshingly dry (at least in the emotional sense).

Basically, after reading through this midwife's blog (, I started really wondering about the potential hiccups during L&D. It really is a dance which should go smoothly under most circumstances. However, I keep coming back to cranium size. If most infants have skulls ranging from 10-11 cm in diameter (13.5" in circ), and the human pelvis is built to accommodate such a head size, what happens when an infant's skull is 15-16" in circ (~12.5 cm diameter)? What's more, what if said baby's head doesn't "tuck" for delivery as it should because of a chain-reaction "drag effect" at another portion of the birth canal? My son tried to come, not crown first where the fontanels would have done their job to aid in compression, but forehead-first -- the strongest part of an newborn's cranium (the bruising patterns on the heads/faces on the infants in similar stories I've encountered suggest a similar position).

Another thing I've been wondering about has been age at onset of first childbirth. (I know I've mentioned this before, but I'm trying to flush it out a bit). In forensics, we can age a skeleton most effectively by, of all things, the pelvis. There's a lot of talk on natural birthing forums about how the pelvis expands to accommodate the baby. This is largely true. However, there's a key technical factor that I've been pondering for a while.
We talk a lot in anthropology about epipheses. These are the "caps" of the long bones which are attached to the long bones by springy cartilage. Instead of thinking of a appendage (such as the leg as "double long bone" (tibia + fibula), cartilage, patela, cartilage, femur; on an individual under 24 it's more like this: talar (ankle) cap, cartilage, tibia shank, cartilage, tibial cap, cartilage, patela, cartilage, femoral cap, cartilage, femoral shank, cartilage, femoral cap get the picture. So we know a human reaches maturity when that cartilage between the long bone shanks and caps calcifies and fuses into bone.
The pelvis has a similar construction. However, in this case, the pubic symphesis (the cartilage connecting the two sides of the pelvis, which expands to accommodate the child's head) does not fuse altogether. The deal is, if childbirth has occurred, in the forensic world we can spot it because the symphesis has permanently stretched out. Regardless, around the same time the epiphesis on the long bones fuse, the symphesis looses some of it's elasticity. This is where my questions start to arise. Historically, most women had delivered their first child prior to this determinate age. Consequently, the symphesis would be at it's most elastic during the birth of their first child and only lost it's elasticity after the permanent "stretch" effect (think of spazzed out elastic  - no wonder so many of our moms and grandmas suffer lower back and hip pain/instability). Even if subsequent children are larger or have larger heads, the pelvis has already been stretched out and requires less strain to accommodate said children through the birth canal.
But what about those of us who don't deliver our first child until after that age? I delivered my son at 26. Yes, lots of women successfully vaginally deliver their firstborn after 25. But how many of those are infants with heads greater than 15" in circ?

I have never attributed my CS to "big baby". I think too often we lump together "big head" and "big baby" as the same issue. However, I believe they are different. My mom delivered my 6lb 14oz sister at 20 and my 8lb 10oz, 22" bro (same size as my son) at 22. However, she'd already delivered a smaller child first and my bro had a nicely coned, 13" head. I think my struggle was due to a combination of factors: delivery after elasticity loss; head circ, and head position.

I agree that only about 10% of women have CS' (c-sections) out of necessity. Considering all other medical factors (such as HELLP, GD, torn placentas, pregnancy-related cirrhosis, childbirth-related hemophilia, and the slough of other complications that could warrant a medically necessary CS), I'd say those of us with legit head-circ/postion/pelvic "disproportion" only constitute <1% of deliveries. Still, that could be as many as 1 in 100 women and infants who would have been removed from the gene pool a century ago. Fortunately, medical intervention, while grossly overused, does appropriately come to our aid as well.

I'd really like to see a study conducted on head circumference (not infant body size), age of first delivery, and CS rates, as unlikely as that is.

Meanwhile ... I'm really starting to think pitocin is evil. I'm finding that I have a negative response to artificial hormones in general. Birth control made me borderline catatonic and even negatively affected physical aspects of my hormonal balance. And the more I read about pitocin and it's relationship to unnecessary cesarean, I'm starting to think inductions are the greater evil (although at 42+ weeks, I also believe my son's induction was a necessary one). I'm actually suspicious (based on a conversation with another mama) that my 60+ hours on pitocin might be a greater factor in my son's ASD/SPD than vaccines or any other factor ... But that's a whole different can of worms.

So ... sorry, I realize this a tome. Just trying to flush out some thoughts. I was really frustrated by the lack of info I could find specifically about correlation between infant skull size and CS. There is one article available concerning a legit study of the issue, but it was regarding a study in Brazil and the full article was only available to medical students with a subscription to a particular online library.

For what it's worth, my argument has never been to defend CS' in a general sense ... or to even battle for the idea that a baby can be too big for a VBAC. Personally, I think we as a nation oversimplify these controversial questions. It's not about "baby vs. pelvic disproportion." In anthropology of gender and sociobiology (animal world included), we frequently discussed the "risky business" of reproduction, and how females are the choosers in the mammilian world of their mates because even in ideal circumstances, producing offspring is a calculated risk. And that's how I approach my deliveries and child-rearing. Every decision I've made: from induction and eventually delivering CS; to vaccinating; to circumcising DS; to my decision to homeschool ... heck, even how I feed my family, I have researched and weighed the risks, knowing there's no "absolute safe answer." Sadly, I think all fascets of parenting (the important ones anyways) are a gamble. You can be an educated, empowered, and responsible parent and still face unexpected tragedy.

Meanwhile ... I can't stress enough that it's important to not place more importance on the event than the life outcome. My husband and I have had this discussion frequently regarding weddings and marriages. It blows us away how people will pour incredible time and finances in pursuit of a "perfect wedding" ... only for their marriage to fall apart months or years later. Sometimes I wonder if we place too much expectation on the childbirth experience as well. So many times I hear women talking about grieving the birth they longed for and never had. Granted, while I did feel out of control of my body during my delivery of my son, I never felt out of control of the situation. I made the decision to induce. I made the decision to refuse pain meds and labor for 3 days. I opted for CS after 3.5 hours of pushing. I never felt as though someone forced that decision on me. So I was bummed, but I didn't feel as though I'd "missed my chance" or had something stolen from me. Frankly, I was just relieved to be alive - and elated that my son was alive and well. I only wish other cesarean mamas could have the same placid confidence I do. I wish the delight of having their baby could truly outweigh their disappointment in the experience. But I don't think society sets them up for that.