Preeclampsia will seriously affect one pregnant woman in every hundred, usually during her first pregnancy. Sometimes referred to as “toxemia of pregnancy” (in our grandmother’s day it was thought to be caused by a mystery toxin) it is responsible for 10 percent of maternal deaths during pregnancy; 2 percent of all emergency cesarean sections; and it is associated with at least 6 percent of all fetal and newborn deaths in this country.
It usually appears during the second half of the pregnancy, and is more common in either the very young or mature-age groups. Early symptoms of preeclampsia are raised blood pressure, protein in the urine, and some times swelling of the face, hands, and legs. If untreated, the disease can rapidly advance to a life-threatening situation for mother and baby.
In advanced preeclampsia a pregnant woman may suffer from convulsions or hallucinations (these include the flashing lights the Greeks called eclampsia) that are signs of major disturbance in the organs and systems of the mother. Preeclampsia can only be cured by delivery of the baby and the afterbirth.
Professor Shaun Brennecke, director of the Department of Perinatal Medicine at the Royal Women’s Hospital, believes that the disease may be caused by an abnormal response of the mother’s immune system during pregnancy, activated by a defective gene passed down in families.
Professor Brennecke began a joint study with Professor Cooper, and coworker Dr Alan Wilton, to search for the defective gene they think is responsible for causing preeclampsia.
When the baby and the afterbirth are expelled from the womb during birth, symptoms of preeclampsia rapidly disappear. This gave rise to the theory that the disease was triggered by partial failure of the response that allows a mother’s immune system to tolerate the baby’s presence in her body.
Although a fetus represents a “foreign” presence in the mother’s body, her immune system doesn’t usually mount an attack to “reject” the fetus. Medical scientists believe it initially senses the fetus as foreign, but then tolerates it. It would seem that the process of recognition and tolerance must occur where the mother’s tissues meet with those of her baby, i.e. where the placenta joins on to the wall of the womb.
The fact that mothers rarely suffer preeclampsia in further pregnancies also fits the pattern of an immune system response. When it first senses foreign tissue, the maternal immune system is fairly slow to respond, but subsequent encounters produce a more rapid and focused response. This would prevent a recurrence of preeclampsia.
The identity of the defective gene still remains a mystery, and finding it among the three billion letters of the human DNA code won’t be easy. It may be hidden some where in one of the other chromosomal clusters of the human genome, and some of the symptoms of preeclampsia may offer leads to speed up the search.
Professor Brennecke and his colleagues hope that by studying the genes that contribute to symptoms like high blood pressure, protein in the urine, and fluid in the tissues, they may be able to “back-track” through the course of events that characterize preeclampsia, to identify the single gene that triggers it off.
The increase in blood pressure may offer some clues. Blood pressure increases when blood vessels contract; reduced blood flow means poorer oxygenation of the tissues and reduced oxygen and nutrient supply to the growing fetus, retarding its growth.
Births are often induced earlier in preeclamptic pregnancies to avoid life-threatening situations, but preeclamptic babies tend to be smaller and weaker at comparable stages than those from uncomplicated pregnancies.
Poor oxygen supply can also cause liver and brain damage to the mother the “flashing lights” of advanced preeclampsia are a symptom of lowered oxygen supply to the brain. Several different hormones interact to regulate blood pressure and by studying the genes of these hormones in normal and preeclamptic women, it may be possible to identify the specific problem.
Meanwhile, early diagnosis and intervention in preeclamptic pregnancies has greatly reduced the risk in most cases to mothers and their babies. Research has revealed that for some women low-dose aspirin taken throughout the pregnancy may reduce the risk of contracting preeclampsia.