Preeclampsia is a leading cause of maternal morbidity and mortality. Low-dose aspirin prophylaxis reduces preeclampsia risk among high-risk pregnant individuals but remains underused in routine clinical practice. This pragmatic cluster-randomized implementation trial will test whether clinician notification of elevated preeclampsia risk increases aspirin prophylaxis utilization among eligible pregnant individuals receiving outpatient obstetric care.

Clusters will be randomized to clinician notification versus usual care. In the intervention arm, obstetric clinicians will receive notification that a patient is at elevated risk for preeclampsia and a recommendation to consider initiation of aspirin prophylaxis between 12 and 28 weeks' gestation, as clinically appropriate. The intervention does not assign participants to aspirin and does not require any study-mandated medication. All decisions regarding aspirin prophylaxis will remain at the discretion of the treating obstetric clinician and patient.

This study is a pragmatic, cluster-randomized implementation trial conducted across two medical centers. The trial will evaluate whether clinician notification of elevated preeclampsia risk increases utilization of aspirin prophylaxis among eligible pregnant individuals in routine outpatient obstetric care.

Eligible encounters will include pregnant individuals receiving outpatient obstetric care who are identified as having elevated risk for preeclampsia based on a clinical risk prediction model. Clusters, defined as outpatient obstetric clinics, care teams, or clinician groups, will be randomized to clinician notification or usual care.

For encounters assigned to the intervention arm, clinicians will receive a notification indicating that the patient is at elevated predicted risk for preeclampsia. The notification will recommend consideration of aspirin prophylaxis initiation between 12 and 28 weeks' gestation when clinically appropriate and consistent with applicable clinical guidelines. The notification is intended to support clinician awareness and evidence-based preventive care. It does not mandate aspirin use or assign patients to receive aspirin.

Encounters assigned to usual care will proceed according to existing clinical workflows without study-generated clinician notification. The primary outcome will be aspirin prophylaxis utilization, defined by electronic health record evidence of aspirin prescription, active medication list entry, or documented clinician recommendation during the eligible gestational window.

Inclusion Criteria:

• Pregnant individuals receiving outpatient obstetric care at participating medical centers.
• Age 18 years or older.
• Currently pregnant and within 12 to 28 weeks' gestation
• Identified as having elevated predicted risk for preeclampsia as defined by USPSTSF and ACOG criteria
• Receiving care from a clinician, care team, or clinic participating in the randomized implementation trial.

Exclusion Criteria:

• Known contraindication to aspirin prophylaxis documented in the electronic health record.
• Pregnancy beyond the prespecified gestational age window for aspirin prophylaxis implementation at the time of eligibility assessment.
• Not receiving ongoing obstetric care at a participating site.