Page 64 - Summer 2017 Journal

Reading Between the Lines
By Merinda Teller, MPH, PhD
Much Ado about Obstetric Dilemmas
On average,
one in three women in the U.S. currently ends up with a c-section, up from 5 percent in 1970.
When you are an excited mom-to-be, and you know that natural childbirth is important for the health of mother and child, ending up with a cesarean section (c-section) can be disap- pointing and even traumatic. Post-surgery, you may mourn not having a Leboyer-style gentle
1
childbirth experience, or regret the baby’s
missed opportunity to encounter beneficial microbes in the birth canal,2 or stew about the potentially deleterious effects of surgical birth
— but it is a pretty safe bet that you are probably not thinking about how your underperforming womb contributed negatively to human evolu- tion.5 Yet a group of theoretical biologists at the University of Vienna made headlines last year
with just such a hypothesis.6
The Austria-based researchers are interest-
ed in what is known as the “obstetric dilemma,” namely the “longstanding evolutionary puzzle why the pelvis has not evolved to be wider.”6 Apparently this puzzle has been with us since the late Pleistocene era, when increasingly large-headed neonates were greeted by a pelvis previously adapted to the narrower require- ments of bipedalism.7 Notwithstanding strong selection pressure, pelvic evolution seemingly never caught up to those big-brained babies. As a result, according to these researchers, the obstetric problem of “mismatched” fetal heads and maternal pelvises (called cephalopelvic disproportion or CPD) has persisted up to the present day, contributing to the sometimes life- threatening condition of obstructed labor.7
SURVIVAL OF THE UNFITTEST
Under the circumstances of overly large
babies trying to ram their way through the birth canal, c-sections claim considerable credit for coming to the rescue of the beleaguered moth- ers. Given that obstructed labor is a frequent
direct cause of maternal mortality in many lower-income countries in particular, global health experts view increased access to surgical delivery as a life-saving necessity.8 The World Health Organization (WHO) generally suggests that a country’s “ideal” c-section rate should be 10 to 15 percent, although some health research- ers have suggested that high-maternal-mortality countries should set their c-section target at roughly one in five women (19 percent).9
In the United States, of course, we have gone well beyond the WHO’s modest 10 percent threshold. On average, one in three women in the U.S. currently ends up with a c-section, up from 5 percent in 1970.10 C-section rates are twice as high in older mothers (forty years or older) as they are for young mothers under age twenty, and rates rose in the over-forty age group from 30 percent in 1996 to a shocking 50 percent in 2010.11
According to the Vienna research group, the escalating c-section rate is having an “evolution- ary effect.”5 Although the investigators are too polite to criticize surgical intervention, their evolutionary perspective posits that c-sections are allowing women with narrow pelvises to sur- vive birth and “pass on their genes encoding for a narrow pelvis to their daughters,” theoretically ensuring that there will be even more c-sections in the future.5
FUNDAMENTAL LAWS OF HEALTH Underlying the theoretical biologists’ narrative is an assumption that childbirth has always been problematic due to the basic an- tagonism between “neonatal encephalization” and “maternal bipedal locomotion.”12 Other researchers dispute this assumption, however, suggesting that mothers’ pelvic dimensions and fetal growth patterns are exquisitely sensitive to “ecological factors,” including diet.12 These
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Wise Traditions
SUMMER 2017
on your infant’s brain and long-term health
3,4