What is the Cause of Pre-eclampsia?

What is the Cause of Pre-eclampsia?

Pre-eclampsia is a complex, multisystem disorder that remains one of the leading causes of maternal and neonatal morbidity worldwide.

Whilst it affects roughly 5% of pregnancies, it is often dubbed the “disease of theories” because, despite decades of clinical research, we still do not have a single, definitive cause.

However, modern medicine has identified several interlocking biological pathways that trigger the condition. Understanding these causes is essential for early screening and management.

What Causes Pre-eclampsia? The Top 5 Scientific Theories

Current consensus suggests that pre-eclampsia is not caused by one single factor, but rather a “two-stage process” involving the placenta and the mother’s systemic response.

1. Placental Hypoperfusion (The Root Cause)

The placenta is the “engine room” of pregnancy. In a healthy pregnancy, specialized cells called trophoblasts invade the mother’s uterine arteries, widening them to ensure a high-volume blood supply to the fetus.

In pre-eclampsia, this “remodeling” fails. The spiral arteries remain narrow and constricted, leading to:

• Placental Hypoxia: The placenta does not receive enough oxygen.

• Oxidative Stress: The struggling placenta releases “distress signals” (toxic proteins) into the mother’s bloodstream.

• Ischaemia: Tissues begin to suffer from a lack of blood flow, triggering a systemic inflammatory response.

2. Systemic Endothelial Dysfunction

The endothelium is the thin layer of cells lining every blood vessel in the mother’s body. When the placenta releases inflammatory proteins, they attack these cells.

• Vasoconstriction: Blood vessels tighten, causing blood pressure to skyrocket.

• Leaky Vessels: Damaged vessel walls allow fluid to leak into tissues (causing edema/swelling) and allow protein to escape through the kidneys (causing proteinuria).

• Chemical Imbalance: There is a marked decrease in Nitric Oxide (which relaxes vessels) and an increase in Endothelin-1 (which constricts them).

3. The Immunological Theory

Pregnancy is a feat of immunological tolerance—the mother’s body must accept a fetus that is 50% genetically foreign. Pre-eclampsia may represent an “immune rejection” of sorts.

• Cytokine Imbalance: An overabundance of pro-inflammatory cytokines vs. anti-inflammatory ones.

• NK Cell Malfunction: Uterine Natural Killer (uNK) cells, which help guide placental growth, may fail to function correctly, leading to the poor vascular remodeling mentioned above.

4. Genetic and Epigenetic Predisposition

Pre-eclampsia often “runs in the family,” suggesting a strong hereditary component.

• Heritability: If your mother or sister had pre-eclampsia, your risk is significantly higher.

• Specific Genes: Research has identified candidate genes such as STOX1 and ACVR2A that may control how the placenta develops.

• Paternal Factor: Interestingly, the father’s genetics also play a role, as the placenta is formed from both parents’ DNA. A change in partners can sometimes change a woman’s risk profile.

5. Environmental and Metabolic Triggers

Secondary factors can exacerbate the primary placental issues. These “stressors” make the mother’s cardiovascular system more vulnerable to the signals sent by a struggling placenta:

• Pre-existing Conditions: Chronic hypertension, Type 1 or Type 2 diabetes, and kidney disease.

• Obesity (High BMI): Increases baseline inflammation and metabolic stress.

• Multiple Gestation: Carrying twins or triplets places a much higher demand on the placenta, increasing the likelihood of “exhaustion.”

Summary of Pathophysiology

Why Understanding the Cause Matters

While the exact “trigger” remains elusive, identifying these pathways has led to the use of low-dose Aspirin as a preventative measure for high-risk women. By targeting inflammation and blood flow early (before 16 weeks), we can often improve how the placenta forms.

If left unchecked, pre-eclampsia can progress to eclampsia (seizures) or HELLP syndrome, both of which are life-threatening. Fortunately, with regular prenatal screening of blood pressure and urine, most cases are managed safely until delivery.

Note: The only definitive “cure” for pre-eclampsia is the delivery of the placenta, though symptoms can persist or appear for several weeks postpartum.