All of the following factors stimulate angiogenesis in a fetus, except:

Interferon Alpha (INFa) were the first described endogenous inhibitors of angiogenesis, they are anti angiogenic agent. It action is by down regulation of bFGF (b Fibroblast Growth Factor). Thus INFa is used in the treatment of pulmonary, brain and other hemangiomas, angioblastomas and giant cell tumours, all of which produce high levels of bFGF. Ref: Tumour Angiogenesis: Basic Mechanisms and Cancer Therapy By Dieter Marme Norbe Fusening, Page 223; Harrison's Principle of Internal Medicine, 16th Edition, Page 463