This is a prospective observational cohort study of platelet phenotype in pregnant patients at high-risk for the development preeclampsia. Blood samples will be collected prior to the initiation of daily aspirin and again in the second trimester to evaluate for platelet changes during pregnancy in patient's as a result of aspirin use and their association with adverse perinatal outcomes.

Inclusion Criteria (Case Group):

• Pregnant patients receiving prenatal care prior to 17 weeks at NYU Langone Health- Obstetrics & Gynecology Associates
• Age 18-50 years
• Singleton viable gestation
• Pregnant patients at high risk of preeclampsia: Patients meeting USPSTF recommendation for low-dose aspirin (81 mg/day) prophylaxis for preeclampsia based on clinical risk factors (see below)

Inclusion Criteria (Control Group):

• Pregnant patients receiving prenatal care prior to 17 weeks at NYU Langone Health- Obstetrics & Gynecology Associates
• Age 18-50 years
• Singleton viable gestation
• Pregnant patients at low risk of preeclampsia: Patients who do not meet USPSTF recommendation for low-dose aspirin (81 mg/day) prophylaxis for preeclampsia based on clinical risk factors.

Exclusion Criteria (Case and Control Group):

• Allergy to aspirin
• Antithrombotic or antiplatelet therapy
• Anemia (hemoglobin <10 g/dl) or thrombocytopenia (Platelet count <100,000), or thrombocytosis (Platelet count >600)
• Known hemorrhagic diathesis
• Planned delivery outside of NYU

Pregnant people at high and low risk of preeclampsia and other adverse perinatal outcomes.

Individual participant data that underlie the primary results reported in this article, after deidentification (text, tables, figures, and appendices), will be shared with investigators who provide a methodologically sound proposal and whose proposed use of the data has been approved by an independent review committee ("learned intermediary") identified for this purpose. Data sharing will begin 9 months and end 36 months following article publication or as required by a condition of awards and agreements supporting the research. Requestors must execute a data use agreement with NYU Langone Health. Requests may be directed to: christina.penfield@nyulangone.org. The protocol and statistical analysis plan will be made available on Clinicaltrials.gov only as required by federal regulation or as a condition of awards and agreements supporting the research.

Beginning 9 months and ending 36 months following article publication or as required by a condition of awards and agreements supporting the research.

Data will be shared with investigators who provide a methodologically sound proposal and whose proposed use of the data has been approved by an independent review committee ("learned intermediary") identified for this purpose. Requests should be directed to christina.penfield@nyulangone.org. To gain access, data requestors will need to sign a data access agreement.