Preeclampsia

Preeclampsia is new-onset, persistent high blood pressure (systolic ≥140 mmHg and/or diastolic ≥ 90 mmHg), with evidence of organ injury, which develops during pregnancy. The most common sign of organ injury in preeclampsia is the presence of protein in the urine (proteinuria), indicating kidney dysfunction, but many organs can be affected, such as the liver and brain.^[1][2][3][4] It usually occurs later in pregnancy (over 20 weeks gestation) and resolves by 3 months postpartum, although it can also develop after childbirth.^[5]

Preeclampsia can still develop in pregnant people who already have chronic hypertension, so signs of organ injury need to be carefully screened for after 20 weeks gestation.

Preeclampsia is important to identify and manage, as it is a leading cause of maternal and fetal complications (e.g., preterm birth; maternal pulmonary edema, cardiovascular disease, and kidney failure; intrauterine growth restriction or poor fetal growth; fetal death).^[4][6][7] Preeclampsia is unlikely to get better on its own and may worsen without medical interventions. In severe cases, pregnant people experience seizures, at which point the condition is termed eclampsia.

Many pregnant people do not experience any symptoms of preeclampsia. Thus, monitoring for the signs of the condition is important. The main signs are a consistent elevation in blood pressure and protein in the urine. Other signs of organ damage that may be present include a low platelet count (thrombocytopenia), elevated liver enzymes, and increased serum creatinine.

Sometimes, people do experience symptoms, especially when the preeclampsia is severe. These include generalized swelling or swollen feet; new-onset headaches that don’t go away; visual changes (blurred vision and/or partial loss of vision); new-onset shortness of breath; pain in the mid- or right-upper quadrant of the abdomen (may feel like heartburn); reduced urinary output; and even changes in mental status (like confusion or agitation). ^[5] An ultrasound may show fetal signs of preeclampsia, like slowed growth of the fetus, low levels of amniotic fluid, and decreased blood flow through the umbilical cord.^[1][8]

Any change or worsening in the signs and symptoms of preeclampsia should be reported immediately to a clinician, as severe preeclampsia is life-threatening to both the pregnant parent and the baby.

Preeclampsia is diagnosed by the onset of high blood pressure and signs of organ damage after 20 weeks gestation (though very rarely it may occur earlier). The formal criteria for a diagnosis include:

• Blood pressure elevation as follows:
• Systolic blood pressure elevation of ≥140 mmHg or diastolic blood pressure elevation of ≥90 mmHg on two occasions at least four hours apart, OR
• blood pressure elevation of ≥ 160/110 mmHg on two occasions at least several minutes apart
• Proteinuria (≥ 300 mg/24 hours, or protein/creatinine ratio of ≥ 0.3, or +2 by dipstick testing if quantitative measurement is not available)^[1][2][3][4], OR at least one of the following signs:
• Elevated creatinine (>1 mg/dL)^[5]
• Low platelets (<100 x 10⁹/L)^[9]
• Liver dysfunction (elevated transaminases)
• Fluid in the lungs (pulmonary edema)
• Neurological dysfunction (hyperreflexia, visual disturbances, headache)^[5][10]

Delivery of the baby and placenta is the only cure for preeclampsia. As such, the goal of medical management is to reduce the risks for both parent and baby until the time of delivery. The treatments used to meet this goal depend on gestational age and the severity of the condition.^[11][12][13]

If preeclampsia is diagnosed at term (≥ 37 weeks of gestation), labor is induced, usually with the medication pitocin (oxytocin). When preeclampsia is diagnosed preterm and no severe features are present, the parent and fetus are closely monitored (e.g., ultrasounds, blood pressure, bloodwork, fetal nonstress tests). Labor is induced at 37 weeks of gestation, unless severe features develop, in which case medications and/or a preterm delivery (before 34 weeks of gestation) may be necessary.^[14]

Blood pressure medications, such as hydralazine, labetalol, and nifedipine^[15], may be given when blood pressure elevations are severe (usually systolic ≥ 160 mmHg and/or diastolic ≥ 110 mmHg).^[16][15] During and after delivery, magnesium sulfate may be used to prevent seizures.^[6][7][17]

Low-dose aspirin therapy may prevent preeclampsia from developing in people at high-risk for this condition. Treatment usually begins before 16 weeks of gestation and continues throughout pregnancy.^[18][16]PMDI:17443552

Calcium can reduce the risk of preeclampsia, especially if a person’s intake is low.^[10][3] Low intake of calcium is somewhat common, even in the US.^[19] Calcium may help by decreasing smooth muscle contractility and increasing vasodilation, thereby lowering blood pressure.^[20]

Selenium may reduce preeclampsia risk in populations where deficiency is common, such as the UK. Conversely, intake of selenium in North America tends to be sufficient.^[21] Selenium’s mechanism in preeclampsia is unknown, but it is likely related to anti-inflammatory and antioxidant effects.^[12]

Supplementation with vitamin D has shown inconsistent benefits for reducing preeclampsia risk.^{[22] [3][23]} In addition to its vital role in calcium absorption, vitamin D may assist in endothelial repair and angiogenesis.^[22][3]

Depending on a person’s diet, a pregnancy-based multivitamin (commonly called a prenatal) may reduce the risk of preeclampsia, since it contains the above nutrients. These prenatals may also include vitamin B12, magnesium, zinc, and docosahexaenoic acid (DHA), all of which are beneficial in people who are deficient. However, there is a wide variation in the quantity and quality of these nutrients across commercially available prenatals.^[10]

Diet alone does not prevent or treat preeclampsia,^[24][25] but certain dietary patterns may reduce the risk of developing this condition. In observational studies, diets higher in fruits and vegetables, low-fat dairy, whole grains, nuts, legumes, olive oil, and fish, and diets lower in ultra-processed foods were associated with reduced risks of preeclampsia.^[26] Higher fiber intake (25-30 g/day) and high dietary potassium intake (>4.1 g/day) were also associated with reduced preeclampsia risk.^[27] Moreover, fiber (specifically soluble fiber) improves blood markers such as low-density lipoprotein cholesterol (LDL-C). This may decrease the risk of developing cardiovascular disease, for which people who have had preeclampsia are at higher risk.^[28][29]

However, intervention-based trials have failed to consistently show a benefit of dietary changes in either risk reduction or treatment of preeclampsia.^[24][25]

Importantly, sodium (salt) intake is not associated with the development of preeclampsia, despite salt being associated with high blood pressure conditions outside of pregnancy.^[30] Therefore, pregnant people with preeclampsia most likely do not need to restrict salt in their diet.

Weight loss before (and between) pregnancies may reduce the risk of preeclampsia in pregnant people who are overweight or obese.^[31][32] In fact, a higher body mass index (BMI) is associated with a higher preeclampsia risk,^[33] as is gaining a greater amount of weight during pregnancy.^[34]

Exercise is beneficial before and during pregnancy (when not contraindicated), and it may reduce both the risk of excessive gestational weight gain and preeclampsia.^[24][35]

The cause of preeclampsia is not fully understood and likely involves both fetal and maternal factors. Abnormal formation of the placenta (which is influenced by genetics, the environment, and the parent’s immune system) may play a central role in preeclampsia development. The placenta in people with preeclampsia often has narrow blood vessels that do not supply enough oxygen and nutrients to the placenta. In response, the parent’s body releases inflammatory cells and chemicals that can affect blood pressure and organs, causing damage.^[5][36][2]