Preeclampsia is a pregnancy complication defined by new high blood pressure that develops after 20 weeks of gestation, combined with signs that organs are under stress. The key blood pressure threshold is 140/90 mmHg or higher on two separate readings taken at least four hours apart. It affects multiple organ systems and ranges from mild to life-threatening, so understanding exactly what qualifies as preeclampsia matters for recognizing it early.
The Blood Pressure Numbers That Define It
A reading of 140 mmHg systolic (the top number) or 90 mmHg diastolic (the bottom number) or higher, confirmed on two occasions at least four hours apart, meets the blood pressure criteria for preeclampsia. Both readings must occur after 20 weeks of pregnancy. If blood pressure was already elevated before pregnancy or before 20 weeks, the diagnosis is chronic hypertension, not preeclampsia.
When blood pressure reaches 160/110 mmHg or higher, the condition is classified as severe regardless of any other findings. The American College of Obstetricians and Gynecologists (ACOG) states that anyone previously diagnosed with gestational hypertension who hits these severe-range numbers should be reclassified as having preeclampsia with severe features, even without other symptoms.
Protein in Urine Is Not Always Required
Traditionally, preeclampsia required both high blood pressure and excess protein in the urine, called proteinuria. The diagnostic cutoff is 300 mg of protein in a 24-hour urine collection, or a urine protein-to-creatinine ratio of about 0.3. Current guidelines, however, no longer require proteinuria if there is evidence of organ damage elsewhere in the body.
Without proteinuria, the diagnosis can still be made when new-onset high blood pressure appears alongside any of the following: low platelet counts (below 100,000 per microliter), kidney dysfunction (creatinine above 1.1 mg/dL), liver enzyme levels at least twice the normal upper limit, fluid in the lungs, or new neurological symptoms like severe headache or vision changes. This shift in diagnostic criteria is important because some people develop dangerous organ involvement before protein ever shows up in a urine test.
What Counts as Severe Features
Not all preeclampsia carries the same level of risk. The “severe features” designation changes how urgently the condition is managed and often influences the timing of delivery. You meet the criteria for severe features if you have any one of the following:
- Blood pressure of 160/110 mmHg or higher on two readings at least four hours apart
- Platelet count below 100,000 per microliter, which signals the blood’s clotting ability is compromised
- Liver enzymes more than double the normal level, indicating liver strain
- Kidney dysfunction, with creatinine above 1.1 mg/dL or protein excretion of 2 grams or more in 24 hours
- Fluid in the lungs (pulmonary edema), causing significant shortness of breath
- Neurological symptoms such as a severe headache that does not respond to medication, blurred vision, or seeing spots
Many of these changes happen internally before you feel them, which is why routine blood work and blood pressure checks during prenatal visits are designed to catch the condition early.
Warning Signs You Can Feel
Some symptoms of preeclampsia are detectable at home between appointments. A headache that is unusually persistent and does not improve with rest or typical pain relief is one of the most commonly reported warning signs. Vision changes, including blurred vision, light sensitivity, or seeing spots or flashing lights, point to neurological involvement.
Upper abdominal pain, often felt on the right side just below the ribs, can indicate liver stress. Sudden swelling of the face or hands, nausea or vomiting that appears in the second half of pregnancy, shortness of breath, and rapid weight gain of two to three pounds or more in a single week are also red flags. None of these symptoms on their own confirm preeclampsia, but any of them after 20 weeks warrants a prompt blood pressure check and evaluation.
HELLP Syndrome: A Severe Variant
HELLP syndrome is considered a subset of severe preeclampsia. The name stands for hemolysis (red blood cells breaking apart), elevated liver enzymes, and low platelets. Diagnosis requires all three: platelets at or below 100,000 per microliter, liver enzymes (AST) at 70 IU/L or higher, and an LDH level of 600 IU/L or more, which reflects red blood cell destruction. HELLP can develop rapidly, sometimes before blood pressure readings look alarming, making it particularly dangerous. It accounts for roughly 12% of cases where low platelet counts appear during pregnancy.
It Can Develop After Delivery
Preeclampsia is not limited to pregnancy itself. Postpartum preeclampsia most often appears within a few days after delivery but can develop up to six weeks later. The symptoms are identical: severe headaches, vision changes, upper abdominal or shoulder pain, shortness of breath, and significant swelling. Because many new parents expect to feel exhausted and uncomfortable after birth, postpartum cases are easy to dismiss. Sudden weight gain, facial swelling, or a headache that will not go away in the weeks following delivery should not be attributed to normal postpartum recovery.
Who Is at Higher Risk
Several factors increase the likelihood of developing preeclampsia. A history of preeclampsia in a previous pregnancy is one of the strongest predictors. Chronic hypertension that existed before pregnancy also raises the risk substantially, as does kidney disease, autoimmune conditions, and diabetes. First pregnancies, pregnancies with multiples (twins or more), obesity, and maternal age over 35 are additional risk factors. Having a family history of the condition, particularly a mother or sister who had preeclampsia, also increases your odds.
For people with one or more high-risk factors, the U.S. Preventive Services Task Force recommends starting a daily low-dose aspirin (81 mg) after 12 weeks of gestation. Studies show that effective preventive doses range from 60 to 150 mg per day, and most research initiated aspirin before 20 weeks. This simple intervention is one of the few proven ways to reduce the risk, though it does not eliminate it entirely.
How It Differs from Gestational Hypertension
Gestational hypertension and preeclampsia both involve elevated blood pressure appearing after 20 weeks, but they are not the same condition. Gestational hypertension is high blood pressure alone, without proteinuria or signs of organ damage. It becomes preeclampsia the moment organ involvement appears, whether that means protein in the urine, abnormal blood work, or symptoms like severe headache and vision changes. About 15 to 25% of people initially diagnosed with gestational hypertension go on to develop preeclampsia, so the conditions exist on a spectrum rather than as entirely separate diagnoses. This is why gestational hypertension requires ongoing monitoring even when initial lab results look normal.