Low Weight Heparin prOphylaxis for Placental-Mediated Complications of PrEgnancy

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