Purpose of review: The present review examines recent publications concerned with the issue of the number of embryos to replace in an in-vitro fertilization cycle and in doing so concentrates on the proposed selection methods that may allow us to transfer one or two embryos.
Recent findings: A number of techniques that will allow us to ascertain the health and viability of the embryo are discussed. These range from methods to assess embryo morphology to those that require more complex forms of technology. Logically the use of the simple methodology is more abundant. However, there is accumulating evidence that some of the more complex assessment techniques may be ready for a more general use.
Summary: In performing embryo selection we need to develop processes that will be extremely critical, allowing us to limit the number of embryos replaced without detriment to pregnancy rates.