Prophylaxis with low-dose aspirin has been recommended to prevent preeclampsia, the rationale being that hypertension and abnormalities of coagulation in this disease are caused in part by an imbalance between vasodilating and vasoconstricting prostaglandins. Low-dose aspirin therapy inhibits thromboxane production more than prostacyclin production and therefore should protect against vasoconstriction and pathologic blood coagulation in the placenta. Initially, several single-center trials, mostly among women at increased risk for preeclampsia, demonstrated a substantial reduction in the risk of proteinuric hypertension as well as reductions in the incidences of preterm birth, infants small for gestational age, and perinatal death,

This will be a randomized control trial to estimate the efficacy of two doses (80 mg versus 160 mg) of aspirin for prevention of preeclampsia in High-Risk Pregnant Women identified in the first trimester to be at high risk.

Inclusion Criteria:

• Pregnant women presenting prior to 17+0 weeks' gestation.
• Moderate to high risk of preeclampsia.
• One or more of the following: previous history of preeclampsia, antiphospholipid antibodies, pre-existing diabetes, pre-existing hypertension, pre-existing renal disease, autoimmune disease, nulliparity, family history of preeclampsia, elevated BMI > 25, and maternal age <20 or >35.
• Give written informed consent.

Exclusion Criteria:

• Multiple gestations,
• fetal aneuploidy
• major fetal structural anomaly
• bleeding disorder
• allergy to aspirin
• women already on aspirin or heparin.

The population of interest involves women attending the study hospital for antenatal care and delivery

both participants and researchers will be blinded to the intervention given.