Early pregnancy factor.

There have been many attempts to develop a test which can detect a pregnancy between the time of fertilization and the time of implantation. The subject of this review is Morton's "early pregnancy factor", a complex immunological phenomenon which is said to become positive within hours of fertilization. However, many workers have been unable to reproduce these findings and the experimental methods have been severely criticized. Substantial further work is needed before a test of this type can be regarded as suitable for routine clinical practice, if indeed it will ever be possible.