There, scientists set upon the tissue with scalpels, forceps and an array of chemicals to extract its weirdly powerful cells, which storm the uterus like an invading army and commandeer a womans body for nine months to keep her foetus alive. The placenta is the life support system for the foetus. A disk of tissue attached to the uterine lining on one side and to the umbilical cord on the other, it grows from the embryos cells, not the mothers. It is sometimes called the afterbirth: It comes out after the baby is born, usually weighing about a pound, or a sixth of the babys weight.
It provides oxygen, nourishment and waste disposal, doing the job of the lungs, liver, kidneys and other organs until the foetal ones kick in. If something goes wrong with the placenta, devastating problems can result, including miscarriage, stillbirth, prematurity, low birth weight and pre-eclampsia, a condition that drives up the mothers blood pressure and can kill her and the foetus. Increasingly, researchers think placental disorders can permanently alter the health of mother and child.
Given its vital role, shockingly little is known about the placenta. Only recently, for instance, did scientists start to suspect that the placenta may not be sterile, as once thought, but may have a microbiome of its own a population of micro-organisms that may help shape the immune system of the foetus and affect its health much later in life.
Fisher and other researchers have studied the placenta for decades, but she said: Compared to what we should know, we know almost nothing. Its a place where I think we could make real medical breakthroughs.
The National Institute of Child Health and Human Development calls the placenta the least understood human organ and arguably one of the more important, not only for the health of a woman and her foetus during pregnancy but also for the lifelong health of both.
In May, the institute gathered about 70 scientists at its first conference devoted to the placenta, in hopes of starting a Human Placenta Project, with the ultimate goal of finding ways to detect abnormalities, and treat or prevent them.
The placenta establishes a blood supply at 10 to 12 weeks of pregnancy. Ultimately, it invades 80 to 100 uterine vessels called spiral arteries and grows 32 miles of capillaries. The placental cells form minute finger-like projections called villi, which contain foetal capillaries and come in contact with maternal blood, to pick up oxygen and nutrients and get rid of wastes. The tissue formed to exchange oxygen and nutrients would cover 120 to 150 square feet. Every minute, about 20 per cent of the mothers blood supply flows through the placenta.
The front line of the invasion is a cell called a trophoblast, from the outer layer of the embryo. Early in pregnancy, these cells multiply explosively. The trophoblast cells shove other cells out of the way and destroy them with digestive enzymes that induce the cells to kill themselves.
Fishers lab discovered that as trophoblasts invade, they alter certain proteins on their surfaces, called adhesion molecules, to become more motile. Researchers later found that cancer cells do the same thing as they spread from a tumor to invade other parts of the body.
Trophoblasts change in other ways, mimicking cells of the blood vessels they invade. The spiral arteries, which feed the lining of the uterus, become paved with trophoblasts instead of the womans own cells. Invasion and remodelling are essential: If they do not occur, the placenta cannot acquire enough of a blood supply, and the results can be disastrous. One consequence can be pre-eclampsia, a condition that brings high blood pressure and other abnormalities, and can be fatal.
Pre-eclampsia is considered a placental disease: Most women with the illness have abnormally small placentas, and when pathologists examine them after the delivery, they often find blood clots, discolorations and a poorly developed blood supply.
For unknown reasons, the placenta does not form properly and cannot keep up with the demands of the growing foetus. The trophoblasts cannot fully change into artery cells and begin churning out an abnormal array of molecules that jack up the mothers blood pressure and may damage her blood vessels.
The rising blood pressure may be an attempt to compensate by forcing more circulation to the placenta. But it backfires. The only treatment is to deliver the baby, which probably works because it also removes the placenta.
At some hospitals, pathologists who specialise in the placenta examine the ones from troubled pregnancies or sickly newborns, looking for clues to what went wrong. Massachusetts General Hospital also keeps seemingly normal placentas in a refrigerator for about two weeks, until it is clear that the mother and the baby are healthy.
The placenta gives the answer in many term stillbirths, Dr Drucilla J Roberts, a placental pathologist, said. Half of those deaths are never explained, but many of them involve abnormalities in the placenta, including infections or unusual conditions in which the mothers immune system appears to have rejected the placenta.
I cant tell you how important it is to the family just to have an answer, she said. Knowing can help ease the guilt that many parents feel when a child is stillborn.