What Exactly Is Preeclampsia? Symptoms and Risks

Preeclampsia is a serious pregnancy disorder defined by new-onset high blood pressure and signs of organ damage, most often developing after the 20th week of gestation. It affects roughly 4 to 10 percent of pregnancies worldwide and remains a leading cause of maternal and newborn illness and death.¹ Despite decades of research, there is no cure other than delivering the baby and placenta, which puts clinicians in the difficult position of balancing a mother’s deteriorating health against the baby’s need for more time in the womb.

How the Placenta Sets the Stage

The root of preeclampsia lies in the placenta, the temporary organ that forms to supply oxygen and nutrients to the growing fetus. In a healthy pregnancy, blood vessels in the uterine wall called spiral arteries are remodeled early on so they widen and allow blood to flow freely into the placenta. In preeclampsia, that remodeling goes wrong: the spiral arteries stay narrow, restricting blood supply and creating a stressed, oxygen-starved placenta.² Recent work has traced part of this failure to disrupted calcium regulation in the smooth-muscle cells that line those arteries, which prevents the cells from switching into a state that allows the vessels to open up.³

The oxygen-starved placenta then releases substances into the mother’s bloodstream that throw off the balance between proteins that build blood vessels and proteins that block them. One protein in particular, called sFlt-1, rises sharply. It binds to and traps growth factors that the mother’s blood vessels need to stay healthy, starving the vessel lining of maintenance signals. The ratio of sFlt-1 to a growth factor called PlGF tracks with how severe the disease becomes: women with preeclampsia show roughly a threefold higher sFlt-1-to-PlGF ratio compared with women who have uncomplicated pregnancies.^{4 5}

The downstream effect is widespread damage to the inner lining of blood vessels throughout the mother’s body. This endothelial damage tips the balance away from substances that relax blood vessels and toward substances that constrict them, driving up blood pressure and impairing the kidneys, liver, and brain.⁶ The immune system piles on: excessive inflammation and imbalanced immune-cell activity amplify the vascular injury.¹

Symptoms and Warning Signs

Preeclampsia is sometimes called a “silent” condition because it can develop without obvious symptoms until blood pressure is checked at a routine prenatal visit. When symptoms do appear, they range from mild to alarming:

• Headache: persistent and often severe, not relieved by typical pain relief
• Visual disturbances: blurred vision, flashing lights, or temporary blind spots, affecting up to a quarter of women with severe preeclampsia⁷
• Upper abdominal pain: pain under the ribs on the right side, often mistaken for heartburn or gallbladder trouble
• Swelling: sudden puffiness in the face or hands beyond the normal ankle swelling of pregnancy
• Nausea or vomiting: appearing for the first time in the second half of pregnancy rather than the usual first-trimester morning sickness
• Rapid weight gain: several pounds in a matter of days, driven by fluid retention

Not all of these symptoms appear together, and some women with dangerously high blood pressure feel perfectly fine. One case report described a 28-year-old woman at 36 weeks who arrived at the hospital with contractions and no obvious signs of preeclampsia; it was only after an emergency cesarean prompted by the baby’s heart-rate drop that lab work revealed significant protein in the urine, confirming undiagnosed preeclampsia alongside a placental abruption.⁸ That case illustrates why consistent prenatal blood-pressure monitoring matters more than waiting for symptoms.

Early-Onset Versus Late-Onset

Preeclampsia is not a single disease. Clinicians divide it into early-onset (before 34 weeks) and late-onset (at or after 34 weeks), and the two behave quite differently. Early-onset preeclampsia arises from the faulty spiral-artery remodeling described above and tends to produce a sicker placenta, more fetal growth restriction, and more severe maternal complications. Late-onset preeclampsia, on the other hand, is driven more by the mother’s own cardiovascular and metabolic predisposition than by a deeply abnormal placenta.⁹

A comprehensive cohort study comparing the two subtypes found that the early-onset group had significantly higher rates of fetal growth restriction, neurological complications, and serious cardiorespiratory problems in the mother. Babies born to women with early-onset disease also had lower birth scores and higher rates of complications like bleeding in the brain and respiratory failure requiring a ventilator.¹⁰ Gene-expression research confirms the split at a molecular level: early-onset disease shows nearly 3,000 disrupted genes concentrated in metabolic pathways, while late-onset disease shows only about 375 disrupted genes, mostly in immune pathways.¹¹

Late-onset preeclampsia is far more common, but because it tends to be milder and strikes closer to the due date, it is sometimes underestimated. The distinction matters practically: early-onset disease may require very preterm delivery with all the associated risks to a baby’s lungs and brain, while late-onset disease can often be managed until the pregnancy is close enough to term that delivery is safer.

When It Turns Severe

Left unchecked, preeclampsia can cascade into life-threatening complications. The most well-known is eclampsia, the onset of seizures in a pregnant or recently delivered woman with preeclampsia. Magnesium sulfate, given intravenously, reduces the risk of these seizures and remains the standard treatment.¹²

HELLP syndrome is another feared escalation. The name stands for hemolysis (red blood cells breaking apart), elevated liver enzymes, and low platelet count. As HELLP worsens, the likelihood of serious maternal harm rises steeply: roughly half of pregnancies with the most severe class of HELLP syndrome involve significant maternal complications, compared with about 11 percent of severe preeclampsia cases without HELLP.¹³

The brain is especially vulnerable. Preeclampsia can disrupt the normal regulation of blood flow in the brain and compromise the blood-brain barrier, potentially leading to brain swelling, stroke, or a condition called posterior reversible encephalopathy syndrome (PRES).¹⁴ A systematic review of women who had brain imaging found PRES in about half of those with eclampsia and roughly a fifth of those with severe preeclampsia alone. The pooled maternal death rate among these cases was around 5 percent.¹⁵

Who Is Most at Risk

Preeclampsia can strike anyone who is pregnant, including people with no prior health problems. However, certain factors consistently raise the odds. A prospective study of women with chronic high blood pressure found that higher body mass index, a previous history of preeclampsia or eclampsia, systolic blood pressure in the 130-139 range at the first prenatal visit, and chronic kidney disease all independently predicted superimposed preeclampsia.¹⁶ Other well-established risk factors include first pregnancies, pregnancies with twins or higher multiples, diabetes, autoimmune conditions, and maternal age over 35 or under 20.

Racial disparities are stark. Research consistently shows that Black women face a disproportionately higher burden of preeclampsia and its complications. These disparities reflect not just biological risk factors but also structural issues in healthcare access, implicit bias, and delayed or inadequate management of hypertensive disorders during pregnancy.¹⁷ Proposed solutions include telehealth monitoring, quality-improvement initiatives, and direct efforts to reduce structural racism in obstetric care.

What Preeclampsia Means for the Baby

Because preeclampsia restricts blood flow through the placenta, the baby may grow more slowly than expected, a condition called fetal growth restriction. In severe or early-onset cases, the baby may need to be delivered prematurely, exposing it to all the risks that come with underdeveloped lungs, brain, and immune system. As noted in the cohort study on early- versus late-onset subtypes, babies born to mothers with early-onset disease had significantly higher rates of brain bleeds, respiratory failure, and infection.¹⁰

In the most dangerous scenario, preeclampsia can trigger placental abruption, in which the placenta separates from the uterine wall before delivery. This deprives the baby of oxygen and can cause rapid, life-threatening blood loss for the mother.⁸ Longer-term follow-up of children born to mothers with preeclampsia also raises concerns: a population-based cohort study found that term-born children exposed to preeclampsia had about a 60 percent higher rate of hospitalization for metabolic and nutritional diseases and a 50 percent higher rate of blood-related disorders compared with unexposed children.¹⁸

The Aspirin Question

Low-dose aspirin is the most widely discussed preventive strategy for preeclampsia. Guidelines from multiple professional organizations recommend it for women deemed high-risk, typically started around the 12th week of pregnancy. The logic is that aspirin may improve blood flow through the placenta by reducing clotting and inflammation. But the evidence is more nuanced than the guideline recommendations might suggest.

A landmark trial randomized over 2,500 high-risk women to either low-dose aspirin or placebo and found no significant difference in preeclampsia rates: 18 percent in the aspirin group versus 20 percent in the placebo group.¹⁹ A more recent trial from China echoed that result, finding preeclampsia in about 17 percent of both the aspirin and control groups with no meaningful difference in maternal or newborn outcomes.²⁰ Other large trials have shown modest benefit, particularly when aspirin is started before 16 weeks of pregnancy and in women specifically at risk for the early-onset form. The takeaway is that aspirin is probably helpful for some women but is not a reliable shield, and its benefit depends heavily on timing and on which subtype of preeclampsia a woman is at risk for.

How Preeclampsia Is Managed

The only definitive treatment for preeclampsia is delivery of the baby and the placenta. Everything else is about buying time safely. When the disease is mild and the pregnancy is preterm, close monitoring of blood pressure, lab values, and fetal well-being can allow the pregnancy to continue under supervision. When blood pressure spikes or organ function deteriorates, antihypertensive medications and magnesium sulfate to prevent seizures become the front line while preparations for delivery are made.

Magnesium sulfate deserves mention because of its unique role. It does not lower blood pressure; its primary job is to prevent or stop seizures. It works, but it requires careful dosing. Too much magnesium can cause its own problems, including depressed reflexes, breathing difficulty, and rarely cardiac arrest, so women on magnesium sulfate are monitored closely for signs of toxicity.²¹

Preeclampsia After Delivery

Many people assume preeclampsia ends when the pregnancy does. It usually improves rapidly after delivery, but not always, and in some cases it appears for the first time in the days or weeks following birth. Postpartum preeclampsia is diagnosed when new-onset high blood pressure and organ damage develop between 48 hours and 6 weeks after delivery.²²

This catches many women off guard, since they are no longer being monitored as closely as they were during pregnancy. A study at a tertiary care center documented cases of delayed-onset postpartum preeclampsia in women who had entirely uncomplicated pregnancies with no prior diagnosis of high blood pressure or preeclampsia.²³ Severe headaches, visual changes, or upper abdominal pain in the weeks after giving birth should prompt urgent evaluation, not dismissal as typical postpartum fatigue.

Long-Term Cardiovascular Consequences

Perhaps the most underappreciated aspect of preeclampsia is what it signals about a woman’s future health. Having preeclampsia is now recognized as a major independent risk factor for cardiovascular disease later in life. A systematic review and meta-analysis pooling adjusted data found that women with a history of preeclampsia faced roughly four times the risk of heart failure, about two and a half times the risk of coronary heart disease, about twice the risk of stroke, and more than double the risk of dying from cardiovascular causes, compared with women who had uncomplicated pregnancies.²⁴

A large population-based study from Korea confirmed elevated risks for both ischemic heart disease and stroke over long-term follow-up.²⁵ These connections are likely driven by shared underlying mechanisms: the endothelial damage and inflammation that cause preeclampsia may also prime the cardiovascular system for problems years down the line.²⁶ Chronic kidney disease is another lasting risk: research shows that both mother and child may carry increased susceptibility to kidney problems after a preeclamptic pregnancy.²⁷

The practical implication is that a history of preeclampsia should be treated as a red flag in a woman’s ongoing healthcare, prompting regular blood-pressure checks, cholesterol screening, and attention to cardiovascular risk factors well beyond the childbearing years. Many women are never told this.

Emerging Screening Approaches

Current screening for preeclampsia relies on measuring blood pressure, testing urine for protein, and in some centers checking the sFlt-1-to-PlGF ratio in blood. These tools are most useful close to the time the disease appears, which limits how far in advance clinicians can plan. Researchers are now working on earlier predictive methods based on cell-free RNA (cfRNA), tiny fragments of genetic material shed by the placenta and other tissues into the mother’s blood.

Unlike protein markers that mainly reflect what is already going wrong, cfRNA can capture gene-expression changes from the placenta, fetus, and maternal organs throughout pregnancy. A review of cfRNA-based prediction models reported accuracy scores ranging from moderate to very high, with average sensitivity over 70 percent.²⁸ One recent study found that cfRNA signatures could identify early-onset preeclampsia up to 18 weeks before clinical symptoms appeared when blood was drawn in the first trimester, with strong accuracy.²⁹ These tools are still in the research phase and not yet in routine clinical use, but they represent a potential shift from reactive management to early intervention.

Why Preeclampsia Is Uniquely Human

An odd fact about preeclampsia is that it appears to be largely unique to our species. Anthropological research links this to two traits that distinguish human reproduction: we have babies with unusually large, energy-hungry brains, and the human placenta invades the uterine wall more aggressively than in almost any other mammal.³⁰ That deep invasion is necessary to sustain the metabolic demands of a developing human brain, but it also creates the conditions for the spiral-artery remodeling failure that triggers preeclampsia. In a sense, preeclampsia may be a cost of the evolutionary strategy that gave us our cognitive abilities, a vulnerability baked into the way human pregnancy works rather than a random malfunction.