The importance of the junctional zone of the endometrium in human reproduction.

Junctional zone endometrium (JZE) thickness and contractility seem to determine gamete and embryo transportation and implantation. Proper function depends on concentration levels, mode and timing of oestrogen and progesterone production. Most probably, the remodelling of spiral arteries, and the development of endometrium and decidua are also highly dependent on JZE activity. Fibroids that are adjacent to JZE affect JZE contractility contributing to abnormal or failed implantation. Disruption of the JZE continuity provokes adenomyosis, a condition that causes chronic inflammation and fibrosis, which negatively affects the normal function of JZE. Imaging by magnetic resonance imaging and three-dimensional sonography can diagnose JZE abnormal appearance, alterations in thickening and contractility frequency, usually in the advanced stage of the disease. Failures of assisted reproduction, and adverse early pregnancy outcomes have also been associated with abnormal JZE. Altered uterine contractions due to JZE changes are strongly associated with poor reproductive outcome and early pregnancy loss. Endometriosis and adenomyosis prevalently co-exist, with clear relation and negative effects on the JZE. The presence of endometriosis should alert to the possibility of coexisting adenomyosis. Co-existence of endometriosis may mask the extent of the negative impact of adenomyosis in infertility.