Pregnant women at a higher risk for pre-eclampsia (PE) should be offered preventive daily treatment with acetylsalicylic acid (ASA) started before 16 weeks of gestation. To select patients at higher risk for PE, multiparametric assessment combining maternal history, biochemical factors and biophysical factors should be used during the first trimester of pregnancy. Multiparametric risk assessments have a detection rate for early-onset PE around 80% at a false positive rate of 10%. Owing to the low prevalence of early-onset and preterm PE, more than 90% of patients considered at high risk, at the first-trimester screening, will not eventually develop PE. Thus, ASA treatment would be innecessary and could be safely discontinued in these patients.

The sFlt-1 to PlGF ratio has a high negative predictive value for PE during the second and third trimester of pregnancy. Thus, it could be used to detect false-positive patients from the first-trimester screening.

This is a multicentric, randomized, open, parallel, controlled, phase III trial, where 1,080 patients under treatment with ASA for being at high risk for preeclampsia from the first-trimester screening, will be candidates to participate. Patients with a sFlt-1/PlGF <38, from 24 to 27+6 weeks of gestation will be randomized at a 1:1 ratio and allocated to either continue ASA until 36 weeks or to stop ASA treatment.

The main objective of the study is to demonstrate that in patients considered to be at high risk for PE (from the first-trimester screening) and with sFlt-1/PlGF ratio <38, between 24+0 and 27+6 weeks, the incidence of preterm PE, after cessation of the treatment with ASA, will not be superior to that of the control group.

Inclusion Criteria:

• Patients older than 18 years old
• Gestational age between 24+0 and 27+6 weeks
• Single pregnancy
• High-risk for pre-eclampsia from the first-trimester screening for pre-eclampsia
• ASA treatment started before or at 16+6 weeks of gestation
• Maternal sFlt-1/PlGF ratio at 24+0-27+6 weeks of gestation
• Signed informed consent

Exclusion Criteria:

• Multiple pregnancy
• Dead and/or fetal polymalformation, including also any fetal genetical and/or chromosomic disease.
• Von Willebrand disease.
• ASA intolerance and /or allergy
• Peptic ulcer
• ASA compliance <50% before inclusion
• Patients with misunderstanding or not able to understand the protocol, including also any condition which could compromise the compliance of the protocol, according to the investigator's opinion.
• No signature of the informed consent