Abstract Objective: to verify if low molecular weight heparin(LMWH) could increase pregnancy rates and/or decrease abortion rates in women with thrombophilia undergoing assisted reproduction cycles. Design: Retrospective study. 30 Setting: Private infertility clinic. Patients: Patients submitted to assisted reproduction (total n=104). Women without thrombophilia (controls, n=20), women with thrombophilia (untreated group, n=30), and women with thrombophilia, treated with daily enoxaparin from the day of embryo transfer until week 36 of gestation (treated group, n=54). Interventions: Enoxaparin treatment for diagnosed thrombophilia. All women underwent controlled ovarian hyperstimulation, in vitro fertilization was performed by intracytoplasmic sperm injection, embryos were transferred on day three. Pregnancy was detected by β-hCG (biochemical) and fetal heart beat at weeks 5-6. Ongoing pregnancy was determined by ultrasound on week 12. Main Outcome Measures: Implantation rate, ongoing pregnancy rate, live birth rate, early pregnancy loss rate, and abortion rate. Results and conclusion: Patients in the Untreated Thrombophilia group presented significantly lower ongoing pregnancy rates and live birth rates, and significantly higher early pregnancy loss and abortion rates when compared to the Control or the Treated Thrombophilia groups. In women with diagnosed coagulation disorders, use of low molecular weight heparin is important in order to avoid miscarriages.7 Keywords: female infertility; thrombophilia; enoxaparin; abortion; in vitro fertilization