Pregnant women at higher risk for preeclampsia (PE) are currently recommended to take low-dose aspirin (acetylsalicylic acid, ASA) daily from the first trimester until 36 weeks of gestation. High-risk women are identified through a multiparametric first-trimester screening that combines maternal history, blood pressure, uterine artery blood flow, and placental growth factor (PlGF). Although this screening effectively identifies women at risk, the majority of those classified as high risk will not develop PE. As a result, a large proportion of pregnant women receive prolonged aspirin treatment without benefit, while remaining exposed to its potential side effects, including increased bleeding risk.

Aspirin prevents PE primarily by improving placental development during the first half of pregnancy. Whether continuing ASA beyond 24-28 weeks provides additional protection remains unclear. A previous randomized trial demonstrated that stopping ASA at 24-28 weeks was non-inferior to continuing until 36 weeks in a predominantly European population. However, whether this finding applies to more diverse populations, including women of African origin who carry a substantially higher baseline risk of PE, has not been established.

This is a multicenter, randomized, open-label, parallel-group, phase III non-inferiority trial conducted across sites in Europe and Africa. A total of 15,160 pregnant women at high risk for PE from first-trimester screening, currently under ASA treatment, will be randomized in a 1:1 ratio before 28 weeks of gestation to either discontinue ASA at 24-28 weeks or continue ASA until 36 weeks of gestation.

The primary objective of the study is to demonstrate that in pregnant women at high risk for preeclampsia from first-trimester multiparametric screening, the incidence of preterm PE after discontinuation of ASA at 24-28 weeks of gestation is non-inferior to that of the control group, who continue ASA until 36 weeks.

Inclusion Criteria:

• Age 18 years or older at time of enrollment.
• Singleton pregnancy.
• Ability to read and understand the informed consent form.
• Having undergone first-trimester preeclampsia screening between 11+0 and 13+6 weeks of gestation using a validated multiparametric algorithm (FMF algorithm at a risk cutoff of 1:100, or Gaussian algorithm at a cutoff of 1:170) and being classified as high risk for preterm preeclampsia.
• Currently taking aspirin 150 mg/day initiated after first-trimester high-risk classification, in accordance with standard clinical practice.
• Voluntary signing of the informed consent form and willingness to comply with the study requirements, including acceptance of the assigned aspirin treatment duration, additional blood tests, and additional ultrasound assessments.

Exclusion Criteria:

• Early pregnancy loss, intrauterine fetal death, or fetus with major structural malformations diagnosed at the time of enrollment.
• Fetus affected by a known genetic or chromosomal disease.
• Contraindication, allergy, or intolerance to aspirin (acetylsalicylic acid).
• Any medical condition that makes aspirin discontinuation unsafe or impossible (e.g., antiphospholipid syndrome, mechanical heart valve, or other conditions requiring indefinite antiplatelet or anticoagulant therapy).

Upon publication, anonymized data will be deposited in the VHIR's institutional open research data repository.