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Health A-Z

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Harvard Medical School

What Is It?

Preeclampsia is a condition that occurs only during pregnancy, and usually only after the 20th week. A woman with preeclampsia develops high blood pressure and protein in her urine, and she often has swelling (edema) of the legs, hands, face, or entire body. When preeclampsia becomes severe, it can cause dangerous complications for the mother and the fetus. One of these complications is eclampsia, the name for seizures that are associated with severe preeclampsia.

Experts are still not entirely sure what causes preeclampsia, but recent research has provided some good clues. The best hypothesis is that preeclampsia occurs when the placenta does not anchor itself as deeply as expected within the wall of the uterus during the first trimester. What causes this abnormal anchoring is unclear, but it may be influenced by the mother's or father's genes or the mother's immune system, and medical conditions the mother may have, such as diabetes or high blood pressure.

Regardless of its cause, early abnormalities in placental formation lead to changes that later affect blood vessels and other organs. Arteries throughout the body can tighten (become narrower), raising blood pressure. They can also become "leaky," allowing protein or fluid to seep through their walls, which causes tissues to swell. In preeclampsia, changes in arteries decrease the blood supply to the fetus and placenta, and to the woman's kidneys, liver, eyes, brain, and other organs.

In parts of the world with more limited medical care, preeclampsia and eclampsia cause many women to die during pregnancy. Fortunately, with appropriate prenatal care and monitoring, most women with preeclampsia and eclampsia and their babies survive just fine.

Eclampsia and, especially, death from preeclampsia are very rare in well-resourced countries like the United States. However, even with the best care, preeclampsia is a leading cause of illness for mothers and newborns. The following conditions increase the chance that a woman will develop preeclampsia:

  • Chronic (long-lasting) high blood pressure

  • Obesity

  • Diabetes

  • Kidney disease

  • Being under 15 years old or over 35 years old

  • It being the woman's first pregnancy

  • Having had preeclampsia in a previous pregnancy

  • Multiple gestations: twins, triplets, or a greater number of multiples (These pregnancies have more placental tissue. This suggests that the placenta or things it produces may play a role.)

  • Certain autoimmune conditions, including antiphospholipid antibody syndrome and some autoimmune arthritis conditions

  • African-American or Hispanic ethnicity

  • Having a sister, mother, or daughter who had preeclampsia or high blood pressure during pregnancy

  • Having a male partner whose previous partner had preeclampsia (this suggests that the father's genetic material, passed to the fetus and its placenta, may play a role)

  • Having a male partner with whom you were sexually active for only a short length of time prior to becoming pregnant (this may be due to a change in the way a woman's immune system reacts to genes from the father after repeated exposure to his semen)

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From Health A-Z, Harvard Health Publications. Copyright 2007 by the President and Fellows of Harvard College. All rights reserved. Written permission is required to reproduce, in any manner, in whole or in part, the material contained herein. To make a reprint request, contact Harvard Health Publications. Used with permission of StayWell.

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