Why Does Preeclampsia Happen?

Reviewed on 3/9/2021

Preeclampsia is caused by abnormal development of the placenta early in pregnancy but it is unclear why this happens. Symptoms of preeclampsia include high blood pressure, excess protein in the urine, water retention (swelling), headache, fatigue, and others.
Preeclampsia is caused by abnormal development of the placenta early in pregnancy but it is unclear why this happens. Symptoms of preeclampsia include high blood pressure, excess protein in the urine, water retention (swelling), headache, fatigue, and others.

Preeclampsia is caused by abnormal development of the placenta early in pregnancy but it is unclear why this happens.

One theory is that in some women the placenta produces factors such as specific proteins or placental “debris” that enter the mother’s blood circulation and are believed to result in the signs of preeclampsia (high blood pressure, kidney, liver and blood clotting abnormalities).  

Risk factors for developing preeclampsia include:

  • Obesity (BMI 30 or greater)
  • First pregnancy (not including miscarriages and abortions)
  • History of preeclampsia
  • Gestational diabetes
  • Family history of preeclampsia in a sister or mother
  • Women carrying multiples (e.g., twins or triplets)
  • Chronic high blood pressure, kidney disease, lupus, or diabetes prior to pregnancy
  • Age under 20 years or over 40 years
  • Vitamin B12 deficiency

What Is Preeclampsia?

Preeclampsia is a condition in which pregnant women have high blood pressure (hypertension) and evidence of organ injury after 20 weeks of pregnancy. It can also occur after delivery (postpartum). The kidneys, the liver, platelets, lungs, and the brain may be affected.

What Are Symptoms & Signs of Preeclampsia?

Preeclampsia may not cause symptoms in some women, so it may be discovered during a prenatal visit, which usually includes a high blood pressure check.

Maternal symptoms of mild preeclampsia include: 

  • Mildly high blood pressure (above 140/90 mmHg and below 160/110 mmHg)
  • A small amount of excess protein in the urine (proteinuria) (0.3 g or more of protein in a 24-hour urine specimen)
  • Water retention

Maternal symptoms of severe preeclampsia include: 

  • Blood pressure of 160/110 mmHg or greater more than once 
  • Persistent severe headache
  • Vision problems (blurred or double vision, flashes of light or squiggly lines, blind spots, vision loss, sensitivity to light)
  • Fatigue
  • Nausea
  • Vomiting
  • Pain in the mid- or right-upper quadrant of the abdomen (similar to heartburn)
  • Low platelets
  • New-onset shortness of breath 
  • Urinating small amounts
  • Bruising easily
  • Abnormal kidney tests 
  • Liver abnormalities 
  • Fluid in the lungs
  • Seizure 

Preeclampsia can also affect the fetus. Effects on the fetus may include: 

  • Slowed fetal growth 
  • Abnormal testing of fetal well-being (for example, a nonreactive nonstress test or low biophysical profile score)
  • Decreased amount of amniotic fluid 
  • Decreased blood flow through the umbilical cord

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How Is Preeclampsia Diagnosed?

A pregnant woman’s blood pressure is checked routinely in prenatal visits. 

If the blood pressure reading is 140/90 or higher, especially after the 20th week of pregnancy, documented on two occasions, at least four hours apart, preeclampsia may be diagnosed. Urine tests may be indicated to check for the presence of protein in the urine. 

Additional tests may also be indicated:

  • Blood tests 
    • To check for kidney or liver dysfunction 
    • Complete blood count (CBC) to check platelet levels and red blood cells
  • Ultrasound to assess fetal size 
  • Fetal heart rate check

A physical exam will also be performed to check for:

  • Abdominal tenderness 
  • Swelling in the mother's face, hands, or legs 
  • Enlarged liver
  • Vision problems

What Is the Treatment for Preeclampsia?

The definitive treatment and cure for preeclampsia is delivery of the fetus and placenta.

  • At term: Pregnancies complicated by preeclampsia at term (37 weeks) are delivered to resolve the condition and minimize the risk to the woman and her fetus from worsening preeclampsia. A fetus at or near term is usually not at high risk of complications.
  • Preterm: When preeclampsia develops before term and the condition is not severe, delivery may be delayed to 37 weeks to allow the fetus time to mature.
    • If severe signs develop, delivery may be necessary to prevent complications in the woman or her fetus.
    • Steroid injections may be given to help accelerate fetal lung development in women who need pre-term delivery (before 34 weeks).
    • Intravenous oxytocin (Pitocin) may be given to induce labor.

High blood pressure and protein in the urine usually go away within a few days following delivery, but it may take a few weeks. 

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Reviewed on 3/9/2021
References
https://www.uptodate.com/contents/preeclampsia-beyond-the-basics?search=Preeclampsia&source=search_result&selectedTitle=2~150&usage_type=default&display_rank=2

https://www.uptodate.com/contents/high-blood-pressure-treatment-in-adults-beyond-the-basics?search=Preeclampsia&topicRef=6720&source=see_link

https://www.nichd.nih.gov/health/topics/preeclampsia/conditioninfo/diagnosed

https://americanpregnancy.org/healthy-pregnancy/pregnancy-complications/preeclampsia-927/

https://www.preeclampsia.org/cause-of-preeclampsia