I read the strangest birth metaphor that truly made me cringe. A scientist likened the growing fetus (our precious unborn babies) to a tumor. A cancer, of all things. It really zapped the beauty and loveliness of pregnancy. During my three pregnancies (including twins), I imagined things closer to seeds flourishing into flowers. Certainly not a malignancy invading my body.
But on second thought, this guy had a point, a quite fascinating one, really. His points get to the heart of an increasingly complicated and contentious debate among a global network of scientists: How do our embryos and fetuses do it? I mean, how do they enter a woman's body and thrive without being destroyed by our immune system. In other words, why doesn't a mother's body treat the fetus as it would, say, a germ or tumor? Why aren't we mounting an immune attack? It's a stunning feat-both by the mother and the embryo. Nothing short of miraculous, really.
The answers to these questions may help women who are infertile, who suffer from multiple miscarriages, or who suffer from dangerously high blood pressure (pre-eclampsia). (And as for the tumor metaphor, the answers may help investigators understand tumor growth.) At the moment, there are no simple solutions, but a few intriguing pathways that may lead to discoveries and eventual treatments.
Harvey J. Kliman, MD, PhD, for one, is an expert on the placenta and a reproductive sciences researcher at Yale School of Medicine and says he has a theory that may help explain how the fetus thrives as a foreignor inside it's mother. He describes pregnancy in war terms, "an absolute battle," with fetus and mother fighting for survival. His ideas hone in on a pregnancy protein called PP13, that he believes serves as a decoy, of sorts. In essence, a flood of PP13 early in pregnancy lures the mother's immune cells to an area of the placenta that is distant from where the fetus is receiving nutrients. His results were published in the in October in the scientific journal, Reproductive Sciences, and reported as well in the New York Times.
"The really novel thing, mind-blowing frankly," said Dr. Kliman, is that "in a normal and completely healthy pregnancy, I saw areas of massive total destruction." He said the necrosis--dead tissue--was in region of the PP13. That certainly does not prove cause and effect, but it hints to a potential mechanism. This protein, he said, has been shown before to play a crucial role in the immune system. And a prior study found that women with low levels of PP13 during pregnancy are prone to miscarry.
The way Dr. Kliman sees it, the onrush of this protein attracts the mother's killer immune cells to one region of the placenta while ignoring the other. And it's in the other place where the baby is growing.
Dr. Koji Yoshinaga, the program director of the reproductive sciences branch of the of the National Institute of Child Health and Human Development, said there are huge gaps in our knowledge about what really happens to during pregnancy to allow babies--these foreigners--to survive within us. We do know that pregnancy hormones change our immune cells, and somehow--perhaps through progesterone or prolactin or other pregnancy chemicals--we are calming the immune responses surrounding the fetus.
Kliman—in addition to his war analogies—likens his theory to bank robbers who get a gang of bad guys to storm the grocery store, just to deflect the cops from the real scene of the crime. Perhaps, he said, PP13 is the decoy that tricks the mom's immune system and keeps the baby thriving.
He may be onto something. But most importantly, is that Drs. Kliman, Yoshinaga and several others of their ilk—whether they are experts in immune cells or pregnancy hormones—are finally joining forces to help us all understand this common yet remarkably complex and mysterious process of gestation.
