The purpose of this research study is to find out whether women with severe preeclampsia taking low-dose aspirin (LDA) for 3 weeks post-delivery will experience an improvement in endothelial function (measured as flow-mediated dilation - FMD) and severity of disease, as the effects of preeclampsia can persist postpartum. Women diagnosed with severe preeclampsia prior to delivery will be enrolled and randomized to receive either low-dose aspirin (81mg) or placebo to take daily for up to 3 weeks post-delivery. Exploratory objective includes healthy control postpartum patients without preeclampsia and not on LDA during pregnancy or postpartum in comparison with the primary study population affected by preeclampsia with severe features.

Preeclampsia is a serious disease of pregnancy that manifests with increased blood pressure and can affect all the organs in a woman's body. It usually develops after 20 weeks of pregnancy. There is an abnormal amount of protein in the urine and with worsening disease known as "severe features," patients can have pain in the upper abdomen, changes in vision, fluid in the lungs, an intense headache, low number of platelets in the blood, and abnormal liver or kidney function. Very high blood pressure is also considered a severe feature. The exact cause of preeclampsia is unknown but women with the condition are at increased risk for complications during pregnancy, including seizures - eclampsia. Babies are at risk of being born premature because the only cure for preeclampsia is delivery. Women who have had preeclampsia are also at increased risk of cardiovascular and kidney disease later in life, including heart attack, stroke and high blood pressure. Studies show that women at high risk for preeclampsia, i.e., have had preeclampsia in a prior pregnancy, are carrying more than one fetus, have a history of high blood pressure, kidney disease or both, have certain medical problems such as diabetes, thrombophilia or lupus, have a modestly decreased risk of disease with daily intake of low-dose aspirin starting after 12 weeks of pregnancy.

Due to the limited data available on the topic of LDA in preeclamptic patients in the postpartum period, particularly as applicable to the American population, the investigator intends to start with a small pilot study involving the collection of information on 10 women not exposed to study intervention. This will allow for confirmation of the sample size based on the baseline FMD measurements 2 days after delivery.

Investigator will also explore a small sub-study to gather information regarding baseline FMD and biomarker values for healthy control postpartum patients, unaffected by preeclampsia and not on LDA during pregnancy or postpartum.

Inclusion Criteria:

• Singleton or Multiple gestation
• Maternal age >= 18 years
• 20 0/7 weeks gestation or greater
• Severe Preeclampsia diagnosed prior to delivery

Exclusion Criteria:

• Aspirin use postpartum for other medical indication
• Lovenox, unfractionated heparin, or other anticoagulant use postpartum for an indication other than postoperative (in-house)
• Aspirin use within 7 days of planned initial FMD testing postpartum
• Hypersensitivity or allergy to Aspirin or other salicylates
• Hypersensitivity or allergy to nonsteroidal anti-inflammatory drugs (NSAIDs) - exception if taking LDA in pregnancy
• Nasal polyps
• Gastric or Duodenal ulcers, history of GI bleeding
• Severe hepatic dysfunction
• Bleeding disorders and diathesis
• Breastfeeding a newborn with low platelets (NAIT)

For sub-study patients, inclusion and exclusion criteria will be the same, with the exception of diagnosis of severe preeclampsia prior to delivery (exclusion criterion for healthy controls group).