Chronic hypertension affects 1–5% of women of childbearing age. During pregnancy, chronic hypertension is associated with an increased risk of vascular disease such as superimposed preeclampsia (PE), intrauterine growth retardation (IUGR), placental abruption, and preterm delivery. These serious and frequent pathologies, specific to pregnancy, carry a particularly high risk of maternal complications (HELLP syndrome, eclampsia, maternal death) and perinatal complications (perinatal death, neurological disorders). To date, there is no curative treatment of vascular complications of chronic hypertension during pregnancy. The only effective treatment, once the complications are established, is usually stopping the pregnancy and delivering the placenta. Some recommendations suggest the use of low dose aspirin in the prevention of these complications. Although the efficacy of low-dose aspirin is assumed in patients with previous preeclampsia, few studies have evaluated its efficacy in patients with chronic hypertension. Controlled prospective studies using very low doses of aspirin (less than 100 mg) and started after 15 weeks of gestation do not seem conclusive.

The objective of this work is first to detail the complications of chronic hypertension during pregnancy, then to analyze the studies which evaluated the interest of low dose aspirin in prevention of the placental vascular complications of the pregnancy in patients with chronic hypertension. We also propose an update on the European and North American national recommendations for the prevention of preeclampsia by low dose aspirin in the high-risk population of patients with chronic hypertension. Finally we present the CHASAP (Chronic Hypertension and Acetyl Salicylic Acid in Pregnancy) trial (NCT04356326), a multicentric prospective randomized double-blind superiority trial, which will compare, in pregnant women with chronic hypertension, the efficacy of low dose aspirin (150 mg/day) with a placebo, in the prevention of maternal-fetal morbidity and mortality (preeclampsia, placental abruption, IUGR, perinatal death, maternal death, and preterm delivery).