Only 23% of women will begin a successful pregnancy during the first menstrual cycle in their attempt to conceive. A large number of these failed reproductive attempts are attributed to a broad set of pathologies, but across studies an important proportion of unsuccessful cycles is consistently left unexplained. Stress has become a commonly cited factor when discussing unexplained reproductive failures. Early research on the effect of stress on reproduction was plagued with methodological problems and lacked a solid theoretical framework. However, recent experimental, clinical and population-based research provides new evidence and suggests novel biological mechanisms, which merit a fresh evaluation of the purported association. Here we briefly review the latest advancements in the study of the interplay between stress, the immune system and women's reproduction, discuss a proposed evolutionary origin for their relationship and examine the biological pathways that may mediate the connection between these three systems.
