It is widely acknowledged that the responsible introduction of new assisted reproductive technologies (ARTs) requires preclinical safety research, including the use of animal models and human embryos. However, the moral sensitivity of human embryo research has led to regulations and guidance stating that human embryos may only be used for research that cannot also be conducted with animals. We call this the 'use animals first' (UAF) rule. In the field of ART research, this translates into the notion of an ideal chain of consecutive preclinical research steps, where research using human embryos may only be considered as a further step after promising results have been obtained in animals first. This may lead to research ethics committees requiring animal studies that are in fact a waste of time and money, while exposing animals to an infringement of their wellbeing for no good purpose. In this paper, we explore the possible moral arguments behind the UAF-rule and test their validity. We conclude that there are no convincing grounds for upholding this rule and recommend replacing it.