Table I.

Overview of hypotheses on the intermediate role of the niche on fertility outcomes.

Hypothesis
Detrimental environment for sperm penetration and implantation
1. Niche-related accumulation of intrauterine fluid impairing implantation
2. Altered immunobiology and/or increased inflammation when a niche is present
3. Distorted contractility of the uterus caused by fibrosis or interruption of the myometrial layer at the site of the niche
4. Accumulation of mucus and old blood in the niche, which may impair sperm penetration
Physical barrier for embryo transfer and implantation
5. A large niche in combination with a strongly retroflexed uterus impairs accessibility for an eventual embryo transfer due to a distorted anatomy
Psychogenic causes that reduce the likelihood of pregnancy
6. Niche-related gynaecological symptoms may interfere with sexual intercourse, and focused therapies for niche complaints may interfere with opportunities to conceive during the convalescence period