Preeclampsia is diagnosed when blood pressure reaches 140/90 mmHg or higher after 20 weeks of pregnancy in someone who previously had normal readings. The top number (systolic) at or above 140, or the bottom number (diastolic) at or above 90, is enough to meet the blood pressure threshold. This reading must be confirmed on at least two separate occasions, taken more than four hours apart, before a diagnosis is made.
The Specific Blood Pressure Numbers
Preeclampsia has two tiers of blood pressure severity, and the distinction matters because it changes how urgently you need treatment.
- Preeclampsia: systolic blood pressure of 140 mmHg or higher, or diastolic blood pressure of 90 mmHg or higher, confirmed on two readings at least four hours apart.
- Severe preeclampsia: systolic blood pressure of 160 mmHg or higher, or diastolic blood pressure of 110 mmHg or higher, confirmed on two readings at least four hours apart.
Only one of those numbers needs to cross the threshold. If your top number is 165 but your bottom number is 85, that still qualifies as severe. These thresholds are consistent across major guidelines from the U.S., U.K., and Canada, with only minor differences in how confirmation timing is handled.
Blood Pressure Alone Isn’t the Full Picture
High blood pressure is necessary for a preeclampsia diagnosis, but it’s not sufficient on its own. That’s what separates preeclampsia from gestational hypertension, which is simply elevated blood pressure during pregnancy without signs of organ involvement. Preeclampsia means the high blood pressure is paired with evidence that the condition is affecting other parts of the body.
Traditionally, protein in the urine was considered mandatory for diagnosis. That’s no longer the case. Current guidelines recognize that preeclampsia can be diagnosed without protein in the urine if other signs of organ stress are present, including low platelet counts (below 100,000), elevated liver enzymes at twice the normal level, or kidney function changes. Between 15% and 46% of cases initially classified as gestational hypertension eventually progress to preeclampsia, which is why close monitoring of blood pressure alone isn’t enough.
Warning Signs Beyond the Numbers
Blood pressure readings happen at your prenatal appointments, but preeclampsia can escalate between visits. Certain symptoms signal that the condition may be worsening, even if your last reading was borderline.
The most important ones to recognize: a severe headache that doesn’t respond to typical pain relief, blurry vision, dark spots in your vision, and light sensitivity. These reflect changes in blood flow to the brain and eyes that can develop quickly. Sudden swelling in the face or hands, pain in the upper right abdomen (where the liver sits), and shortness of breath are also red flags. Any of these symptoms alongside known elevated blood pressure warrants immediate evaluation at a hospital, not a phone call to schedule an appointment.
When and How Blood Pressure Is Monitored
Blood pressure is checked at every prenatal visit throughout pregnancy. If a single reading comes back elevated, it gets repeated to rule out a temporary spike from stress, rushing to the appointment, or other transient causes. The U.S. Preventive Services Task Force and the UK’s National Institute for Health and Care Excellence both recommend blood pressure measurement plus a urine check for protein at every prenatal visit as standard screening.
If you’ve been diagnosed with a hypertensive disorder during pregnancy, monitoring continues after delivery. ACOG recommends a blood pressure check no later than 7 to 10 days postpartum for anyone who had elevated readings during pregnancy. For those with severe hypertension, that follow-up should happen within 72 hours of leaving the hospital. Home blood pressure monitors can be useful during this period, but any reading at or above 140/90 should prompt a call to your provider.
Postpartum Preeclampsia
Preeclampsia doesn’t always end with delivery. Postpartum preeclampsia can develop in the first few days after birth or appear as late as six weeks postpartum, sometimes in people who had completely normal blood pressure during pregnancy. The same blood pressure threshold applies: 140/90 or higher. This is why hospitals typically check blood pressure multiple times before discharge and why postpartum follow-up visits exist.
The challenge is that many new parents attribute headaches, swelling, and fatigue to normal recovery from childbirth. A persistent severe headache, visual changes, or upper abdominal pain in the weeks after delivery deserve the same urgency as they would during pregnancy. Postpartum preeclampsia is less common than the prenatal form, but it carries real risks precisely because it’s easy to dismiss the symptoms.
How Gestational Hypertension Differs
If your blood pressure hits 140/90 after 20 weeks but there’s no protein in your urine and no signs of organ involvement, the diagnosis is gestational hypertension rather than preeclampsia. The blood pressure numbers are identical. The difference is entirely about what else is happening in the body.
This distinction isn’t always permanent. Research shows that a significant portion of gestational hypertension cases, potentially up to nearly half, eventually evolve into preeclampsia. That progression can happen over weeks or quite rapidly. This is why a diagnosis of gestational hypertension still means closer surveillance: more frequent blood pressure checks, repeated urine tests, and blood work to catch early signs of organ stress before they become dangerous. A blood pressure reading that was “just” gestational hypertension at 28 weeks may look different at 34 weeks with new lab findings.