This is a Multicenter, randomized, open-label, parallel groups study to test the hypothesis that prophylactic low molecular weight heparin (LMWH) (enoxaparin) initiated before 14 weeks of gestation could improve maternal and perinatal outcome in women at high risk for developing placental-mediated pregnancy complications.

Inclusion Criteria:

• Pregnant women ≥18 years

• Gestational age < 14 weeks at randomisation

• One or more of the following complications in a previous pregnancy:

  • Severe PE resulting in delivery before 32 weeks of gestation
  • Newborn weight less than the 10th percentile and documented abnormal Doppler in the umbilical artery during pregnancy before 32 weeks gestation
  • Abruption of placenta
  • Unexplained intrauterine death between 20-41,6 weeks of gestation secondary of placental insufficiency or

• Uterine arteries Pulsatility Index (mPI) Doppler ≥95th percentile at 11-14 weeks of gestation.

Exclusion Criteria:

• Multiple pregnancy
• Abnormal thrombophilia study
• Alcohol or illicit drug use
• Severe fetal malformations or chromosomal abnormalities
• Previous history of infertility ( 3 or more early miscarriages)
• Maternal HIV, Cytomegalovirus or toxoplasma infection
• Known fetal abnormality or chromosomal defect at randomisation
• Women with previous venous or arterial thrombotic event
• Organic lesions that could increase the hemorrhagic risk: gastric ulcus, stroke, a recent hemorrhagic event, high risk situations for hemorrhagic event
• Known allergy to heparin or LMWH, thrombopenia or thrombosis episode due to heparin treatment
• Contraindication to LMWH
• An absolute indication for anticoagulant therapy: venous deep thrombosis, pulmonary embolism, ovaric hyperestimulation, cardiophaty, others
• Metabolic disorders a risk for development of PE and/or IUGR: Type I diabetes, hipertiroidism, chronic renal insufficiency