■ WHEN Tom Cruise announced his intention to

eat his wife’s placenta, there was a media frenzy. The average placenta weighs a sizeable half-a-kilo plus, and apparently it tastes like veal.

A quick Google yields a number of recipes, including placental lasagne, meat loaf, even a placental smoothie. It is in demand with vegetarians, for whom it is a rare opportunity to eat meat that does not involve slaughter of any kind. There is even talk of a miraculous skin cream derived from placental extracts.

Perhaps this recent publicity is why the collection of placental samples for research has become fraught of late. Proud new mothers now peer suspiciously at the consent form, wondering what unseemly things you propose to do to their precious afterbirth in the name of science.

The human placenta is a remarkable organ. It is derived entirely from the developing fetus and acts as substitute lungs, stomach, liver and bladder throughout pregnancy. Fetal cells known as trophoblasts invade the

lining of the womb, hijacking the maternal blood system to provide the baby with the oxygen and nutrients needed.

These trophoblasts must maintain a highly selective barrier between maternal and fetal blood to prevent the mother’s immune system from “spotting” the foreign object growing in its midst. This protective layer is in direct contact with the mother’s blood and breakdown would be catastrophic for the baby, which would be treated like an organ transplant and unceremoniously rejected. Some immune cells are able to squeeze through the minuscule space between two cells so the trophoblasts solve this problem by fusing together. This stratagem is rather like holding hands with your neighbours to stop anyone else getting past, and ensures that the baby is “hidden” from the mother’s immune cells.

So how do these fused trophoblasts differ between normal and abnormal pregnancies? One in four pregnancies end in miscarriage and 1 per cent of women suffer from repeated miscarriage. No statistic can adequately convey the heartache and trauma of losing a child, let alone more than one. In cases of recurrent miscarriage, the front-line trophoblasts are the obvious suspects. Any defect in the fusion process would create chinks in the placental armour through which maternal cells could pass with disastrous consequences.

One in 15 pregnancies are complicated by a condition called pre-eclampsia, where the mother suffers from high blood pressure, with serious and potentially fatal consequences for both mother and baby. This is no modern disease. It was documented by the ancient Egyptians and Greeks, and continues to be poorly understood and difficult to treat even today. Research suggests that the fused trophoblasts slough off from

the surface of the placenta into the maternal bloodstream, like the shedding of old skin cells, provoking an immune response from the mother which results in pre-eclampsia.

Why are these cells shed? Why don’t they fuse properly? Can we prevent this? Would that stop miscarriage or pre-eclampsia? These are just some of the key questions I hope my research will answer.

One major problem is that there are many other types of cells besides trophoblasts present in the placenta, which create experimental red herrings. A new technology, called laser capture microdissection, is emerging. This uses a very fine laser beam to cut out microscopic pieces of tissue, even single cells. Using this technique, I will dissect the fused trophoblast layer from the placenta, away from the rest of the sample. I will then

analyse what these cells are actually doing at different stages of pregnancy, a kind of molecular snapshot of what the placenta is up to at that moment. Comparing the cell profiles from normal and diseased placentas may offer some insight into what is going wrong.

The problems of the placenta should concern us all. There is evidence that the diseases of adult life, such as heart disease and diabetes, originate from the initial success or failure of this unique organ. The placenta holds the key to our good health from the time of conception and deserves to be both celebrated and investigated. But I must confess to an embarrassing failure of nerve when it comes to placental lasagne… ●

Katherine Robertson is a PhD student in the department of obstetrics and gynaecology at the University of Cambridge School of Clinical Medicine, UK

DO YOU LIKE IT RARE OR WELL-DONE?For babies, the placenta is an essential life-support system. For adults, it holds clues about the terrible diseases we face. Even so, Katherine Robertson, winner of the 2008 New Scientist/Wellcome Trust essay competition, draws the line at eating it

Knowing how the placenta changes in pregnancy could help prevent miscarriage

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“The problems of the placenta should concern us all”

Essay competition

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