Aspirin Doses for Preventing Pregnancy High Blood Pressure

Inclusion Criteria: 1. live intrauterine gestation ≤16 6/7 weeks gestational age based on best clinical obstetric estimate, 2. age 14 years or older and able to provide informed consent, 3. at least one of the following high-risk criteria: i) any prior pregnancy complicated by preeclampsia ii) current pregnancy complicated by chronic hypertension diagnosed before randomization (ACOG) iii) pre-gestational diabetes (on medication for diabetes prior to pregnancy, or diabetes is diagnosed prior to randomization with hemoglobin A1C of 6.5% or greater or abnormal 3-hour glucose tolerance test) iv) twin gestation (including higher order pregnancy reduced to twins prior to 14 weeks) v) chronic kidney disease vi) autoimmune disease (e.g., antiphospholipid syndrome, systemic lupus erythematous) 4. or two or more moderate-risk criteria for HDP (per USPSTF), i) nulliparity (no prior delivery at or after 20 weeks 0 days of gestation) ii) obesity (body mass index ≥30 kg/m2 at time of randomization) iii) age ≥35 years (at time of expected estimated due date) iv) Black race v) low income vi) personal risk factors (previous pregnancy with low birth weight or SGA infant, previous adverse pregnancy outcome \[unexplained stillbirth\], placental abruption, interval \>10 years between pregnancies) vii) Family history of preeclampsia (i.e., mother or sister) viii) In vitro fertilization 5. patient not currently on aspirin OR patient on aspirin for obstetrical indications (e.g., related to IVF, or HDP) and: i- randomized before 130/7 weeks gestation, or ii- randomized on or after 13 0/7 weeks gestation and started aspirin within 2 weeks prior to randomization (e.g., aspirin started for HDP prevention at 12 0/7 weeks and patient randomized at 13 2/7 weeks). Exclusion Criteria: 1. known allergy or hypersensitivity to aspirin or any medical condition where aspirin is contraindicated (e.g., active peptic ulcer disease, nasal polyps, NSAID-induced asthma, active gastrointestinal bleeding, known G6PD deficiency, severe hepatic dysfunction, bleeding disorders, history of bariatric surgery), 2. current or planned aspirin use in pregnancy for non-obstetrical indication (e.g., prior stroke/prior myocardial infraction), 3. age \< 14 years, 4. involuntarily confined or detained, 5. considered as having a diminished decision-making capacity, 6. obstetrical ultrasound suspicious for major congenital abnormality, known or suspected fetal aneuploidy, fetal demise, or planned pregnancy termination, 7. participation in another trial that affects the primary outcome, without prior approval of the PI, 8. plan to deliver at an outside participating site with inability to obtain medical records, 9. monoamniotic twin gestation because of the risk of fetal demise and preterm delivery, 10. participation in this trial in prior pregnancy, 11. triplet or higher order pregnancy.