Preeclampsia Diagnosis and Management

Pathophysiological Basis

The 20-week cutoff reflects the time when placental development and remodeling of maternal spiral arteries should be complete, with inadequate remodeling being a key pathophysiological mechanism in preeclampsia 1, 2
Before 20 weeks, hypertension is more likely to represent pre-existing or chronic hypertension rather than pregnancy-induced hypertension 3

The International Society for the Study of Hypertension in Pregnancy (ISSHP) defines preeclampsia as gestational hypertension accompanied by one or more new-onset conditions at or after 20 weeks' gestation 1
Hypertension that develops before 20 weeks is classified as pre-existing or chronic hypertension, which has different management implications 3, 4
This classification helps distinguish between pre-existing hypertension, gestational hypertension, and preeclampsia 1, 3

The 20-week threshold helps clinicians differentiate between chronic hypertension and preeclampsia, which have different management approaches and prognostic implications 2, 5
Risk assessment and preventive strategies for preeclampsia, such as aspirin, are recommended to begin before 16 weeks but definitely before 20 weeks, aligning with this pathophysiological timeline 6
Community monitoring for preeclampsia typically begins after 20 weeks since, by definition, preeclampsia cannot be diagnosed before this gestational age 7

Low-dose aspirin should be initiated before 16 weeks but definitely before 20 weeks in high-risk women 6
Calcium supplementation is recommended for women at increased risk with likely low calcium intake 4, 6
Different monitoring schedules are recommended before and after 20 weeks, with women being assessed for signs and symptoms of preeclampsia at each visit after 20 weeks 7