Battle between the placenta and uterus could help explain preeclampsia

A battle that brews in the mother's womb between the father's biological goal to produce the biggest, healthiest baby possible vs. the mother's need to live through delivery might help explain preeclampsia, an often deadly disease of pregnancy. The fetus must be big enough to thrive, yet small enough to pass through the birth canal. In a new study, Yale researchers describe the mechanism that keeps these conflicting goals in balance.

The findings are published in the October 11, 2011 online issue of Reproductive Sciences.

The battle is waged between the mother's uterus and the baby's placenta, which is made up of cells called trophoblasts that are controlled by the father. In the study, led by Harvey J. Kliman, M.D., research scientist in the Department of Obstetrics, Gynecology & Reproductive Sciences at Yale School of Medicine, researchers observed how the placenta tricks the mother so she doesn't attack the trophoblasts that are trying to increase the flow of her blood into the placenta. If this placental deception doesn't work the mother may develop preeclampsia, a condition that results in high blood pressure and protein in the mother's urine. The only known cure for preeclampsia is delivery of the baby.

The placenta's job is to get nutrients from the mother during pregnancy. Kliman explained that in a normal pregnancy, specialized invasive trophoblasts leave the placenta and invade the mother's tissues to attack and destroy the walls of her blood vessels. This allows the most blood possible to enter the placenta, resulting in a big baby.

But the mother's own "soldiers," called lymphocytes, are constantly looking to destroy the invasive trophoblast cells. The placenta in turn appears to trick the mother by creating a diversion to occupy her lymphocytes.

Preeclampsia is a disorder that occurs only during pregnancy and the postpartum period and affects both the mother and the unborn baby. Affecting at least 5-8% of all pregnancies, it is a rapidly progressive condition characterized by high blood pressure and the presence of protein in the urine. Swelling, sudden weight gain, headaches and changes in vision are important symptoms; however, some women with rapidly advancing disease report few symptoms.

Typically, preeclampsia occurs after 20 weeks gestation (in the late 2nd or 3rd trimesters or middle to late pregnancy), though it can occur earlier. Proper prenatal care is essential to diagnose and manage preeclampsia. Pregnancy Induced Hypertension (PIH) and toxemia are outdated terms for preeclampsia. HELLP syndrome and eclampsia (seizures) are other variants of preeclampsia.

Globally, preeclampsia and other hypertensive disorders of pregnancy are a leading cause of maternal and infant illness and death. By conservative estimates, these disorders are responsible for 76,000 maternal and 500,000 infant deaths each year.

The placenta creates this diversion by secreting a protein called placental protein 13 (PP13), also known as galectin 13, into the mother's blood where it travels through her veins into the uterus below the placenta. There the PP13 leaves the veins where it triggers the mother's immune system to react and attack. The entire area around these veins becomes a mass of inflammation and dead cells, called necrosis.