Using Placental Pathology to Prevent Recurrent Adverse Pregnancy Outcomes: A Pilot Project

Eligibility Criteria: Inclusion (must meet all three criteria): 1. Subjects with a prior adverse outcome in a prior pregnancy. Adverse outcome is defined as prior singleton preterm birth ( \< 37 weeks), SGA infant (defined as birthweight \< 10th percentile), preeclampsia with severe features, or stillbirth (fetal demise after 20 weeks gestation), as certified by an obstetrician 2. Patients with maternal vascular malperfusion on pathology from pregnancy with prior adverse pregnancy outcome, as certified by a perinatal placental pathologist 3. Current singleton pregnancy at \<16 6/7 weeks gestational age. Exclusion Criteria: 1. Anticoagulation planned for current pregnancy (including warfarin, enoxaparin, heparin) 2. Known major fetal anomaly 3. Contraindication to enoxaparin: Specifically active major bleeding, known thrombocytopenia (platelets \<100), hypersensitivity to enoxaparin sodium, hypersensitivity to heparin or pork products, hypersensitivity to benzyl alcohol 4. Chronic kidney disease with eGFR\< 60 5. Known chronic liver disease with baseline AST/ALT \> 3 x upper limit of normal 6. Subjects with mechanical prosthetic heart valves