Preeclampsia and High Blood Pressure During Pregnancy

Cause

The causes of preeclampsia and high blood pressure during pregnancy are poorly understood. In fact, preeclampsia is sometimes called the "disease of theories," and its cause is the subject of active research.²

Most experts believe that preeclampsia starts with a poorly developed placenta that doesn't circulate blood normally.³ However, the cause of the placenta disorder isn't yet clear. Nor is it known why the mother's body then develops high blood pressure. So far, a number of possible factors are thought to play a part in preeclampsia, including:

• Family history (genetics). The tendency to develop preeclampsia may run in families. Inherited factors (genes) seem to make a woman more likely to develop preeclampsia. Similarly, men with a family history of preeclampsia are more likely to father a preeclampsia-affected pregnancy than men with no such family history.⁴
• An abnormal immune system response. Preeclampsia occurs most often in women who are pregnant for the first time and in women who have been pregnant before but now have a first pregnancy with a different man.^{3, 5} Experts think that some women may have an immune system reaction that triggers the condition.¹ Exposure to an antigen from the father (in the growing placenta or fetus, for example) may trigger an immune response in the woman's body. This immune response may result in narrowing of the blood vessels throughout the body, causing higher blood pressure and other problems.
• A biochemical factor that causes the blood vessels to narrow, raising blood pressure. Preeclampsia may be the body's reaction to the poorly functioning placenta. Or, both the poorly developed placenta and preeclampsia symptoms may be caused by the same factor. This process is not yet well understood.⁶
• Underlying diabetes or other diseases affecting blood vessels. Conditions that cause blood vessel problems (such as lupus, preexisting high blood pressure, or diabetes) increase the risk of preeclampsia.³

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Author:	Shannon Erstad, MBA/MPH	Last Updated: November 22, 2006
Medical Review:	Joy Melnikow, MD, MPH - Family Medicine William Gilbert, MD - Perinatology
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