one to three top-quality embryos were transferred 48 hours after oocyte retrieval under ultrasound guidance , with a CCD embryo transfer catheter. At the same time , patients (n=86) were randomized to two groups using a computer-generated randomization . Group A ( n=43) included the patients who received unfractionated heparin 5000 IU twice a day subcutaneous injection . Treatment was started from the day of embryo transfer until 14 days after ET . If β-hCG was positive , the unfractionated heparin was continued until 6 weeks postpartum . Group B ( n=43 ) did not receive any antithrombotic drugs.