At what gestational age does preeclampsia typically occur in pregnancy?

Typical Time Frame for Preeclampsia in Pregnancy

Preeclampsia occurs after 20 weeks of gestation by definition, is most common at term (≥37 weeks), but the most severe complications typically develop when it presents before 32 weeks. 1, 2

Gestational Age Distribution

Standard onset window:

• Preeclampsia cannot be diagnosed before 20 weeks of gestation by definition 1, 3
• The condition can occur from 20 weeks of gestation through the postpartum period 1
• Most cases occur at term (≥37 weeks' gestation), when eclampsia is also most common 2

Early-onset disease (before 32 weeks):

• Represents the most serious subset with worst maternal and fetal outcomes 1, 2
• Associated with higher rates of placental abruption, HELLP syndrome (hemolysis, elevated liver enzymes, low platelets), and renal failure 1, 2
• Average interval between diagnosis and delivery is 14 days (range 0-62 days) 1, 2
• A substantial proportion require delivery within 72 hours of diagnosis 1, 2

Late-onset disease:

• HELLP syndrome most commonly occurs between weeks 27 and 37, with 20% of cases presenting within 48 hours of delivery 1
• Eclampsia is most common at term 1, 2

Atypical Presentations

Preeclampsia occurring before 20 weeks is extremely rare and atypical 4, 5, 6:

• Usually associated with molar pregnancy, trophoblastic disease, antiphospholipid syndrome, or fetal chromosomal abnormalities like triploidy 4, 5, 6
• Requires heightened clinical suspicion and investigation for underlying causes 4, 5

Postpartum preeclampsia:

• Can occur from 48 hours to 6 weeks after delivery 3, 7
• Rare cases have been reported up to 12 weeks postpartum 7

Clinical Implications for Monitoring

Before 32 weeks:

• Women with one risk factor should be assessed at least every 3 weeks 1, 2
• This intensive monitoring reflects the higher risk of rapid progression and severe complications 1, 2

After 32 weeks until delivery:

• Assessment frequency increases to at least every 2 weeks for at-risk women 1, 2
• Preeclampsia can progress to life-threatening complications within approximately 2 weeks from diagnosis 1, 2

Critical Pitfall

The absence of antenatal care is strongly associated with eclampsia and fetal death 1. Even women without identified risk factors can develop preeclampsia and require standard monitoring protocols, as the condition can develop between scheduled assessments 1, 2.