The Placenta Is Not a War Zone
Even though a father’s and mother’s genes differ, that doesn’t mean pregnancy is a “battle of the sexes.”
But the Yale group’s story about diversion and attack is not proved by their data—it is neither tested nor easily testable. Indeed, it is possible to look at the same cellular events and spin a less adversarial tale—say, that mother and fetus are collaborating to suppress the mother’s immune response, so that the fetus can do what it needs to do to build a healthy placenta. David Haig of Harvard, who suggests this alternate spin, also points out that by breaking down uterine tissue, placental protein 13 might actually be helping to facilitate the lateral expansion of the placenta, rather than simply causing a violent distraction. (Haig himself is well-known for advancing a conflict-based view of the placenta, though his metaphorical bent is gentler: The fetus makes demands on mother, and mother responds by “setting limits,” much as she’d do with a child, he says.) At the same time, the crucial assumption that Dad’s genes control the placenta and drive its demands on mom is by no means a given—see here, for example.)
The budding relationship between mother and fetus is, to some degree, open to interpretation—or pop psychological projection. Early on, for instance, cells around the embryo produce a hormone called human chorionic gonadotropin, which causes Mom to continue making the progesterone and estrogen necessary to sustain gestation. Fetal signals, acting directly or indirectly, also cause her to eat more and modify her immune responses so she won’t reject the pregnancy. Are these examples of the baby-to-be making bossy demands that will leave mom depleted, exhausted, and immune compromised? Or do they represent a form of exquisite communication, a priming of mother’s body that will help to ensure a healthy nine months?
Or what about this: Shortly before birth, mom’s brain ramps up production of oxytocin, the hormone responsible for uterine contractions. But she doesn’t produce more receptors for oxytocin—which would allow her body to respond and go into labor—until she receives a key signal from the fetal adrenal glands. In essence, the fetus tells Mom when it’s ready to go: “It’s a mechanism to prevent premature labor, before the fetus is fully mature, says Barry Keverne of the University of Cambridge. So again: pushy baby or sweet communication?
Ultimately, a storyline in which synchronicity trumps conflict has a lot to recommend it. Mother, father, and fetus share profound common interests: the success of the pregnancy, the birth of a healthy baby, and the continued survival of Mom. When scientists rev up the warfare rhetoric, it’s easy to forget that both parents are genetically related to baby, and that pregnancy has successfully perpetuated the species for a very long time.
I like a good prenatal metaphor as much as the next mom. But when the imagery gets this sensational, it’s easy to feel trapped in Hollywood clichés. Kliman’s careful, molecular work reveals something new about a key placental protein—why not appreciate it for that? Sometimes unadorned description—in this case, of how a tiny corner of the world really works—can be enough.
Amanda Schaffer is a science and medical columnist for Slate.