Treatment Preventive for Pre-eclampsia by Acetylsalicylic Acid in Women Who Underwent Frozen Embryo Transfer

Inclusion Criteria: * Healthy women from \[18 - 43\] years-old, planned for a frozen embryo transfer, with natural and modified natural or HRT cycle * Who have given their informed consent * Who have a confirmed pregnancy at week 6 of amenorrhea. Exclusion Criteria: * Women presenting one risk factor for preeclampsia: multiple pregnancy, history of preeclampsia, BMI \> 30, lupus syndrome, preexistent proteinuria, non-treated chronic high blood pressure (\>140/90), antiphospholipid antibody syndrome, diabetes (fasting blood sugar \>126mg/dl) * Contraindication to acetylsalicylic acid (at risk of active hemorrhage (like hemophilia, …); at risk of or who have a gastro-duodenal ulcer; at risk or how have a terminal renal or hepatic in-sufficiency (only if acetylsalicylic acid is given at high dose) * Already treated with acetylsalicylic acid * Treatment with anticoagulants or non-steroid anti-inflammatory drugs