Uterine Fibroids and Adenomyosis

Uterine fibroids (leiomyomas) are benign smooth-muscle tumours of the myometrium, and adenomyosis is the presence of endometrial glands and stroma within the myometrium. Both are common, oestrogen-influenced uterine conditions that can contribute to subfertility — fibroids chiefly when they distort the cavity, and adenomyosis through altered junctional-zone function and endometrial receptivity. They are grouped here because both impair fertility by changing the myometrium and the implantation environment.

Definition

Uterine fibroids are benign monoclonal smooth-muscle tumours arising in the myometrium, classified by location (submucosal, intramural, subserosal); adenomyosis is the ectopic presence of endometrial tissue within the myometrium. Both can contribute to uterine-factor subfertility, most clearly when they distort the endometrial cavity or junctional zone.

Scope

This entry covers fibroids and adenomyosis together as myometrial conditions relevant to fertility, summarising their nature, the mechanisms linking them to subfertility, and their epidemiology. It is reference-educational and non-prescriptive; it explains associations rather than recommending specific treatments. The primary MeSH anchor is Leiomyoma; adenomyosis (MeSH Adenomyosis, D062788) is covered as the paired condition.

Core questions

• Which fibroids affect fertility, and how does location matter?
• By what mechanisms does adenomyosis impair implantation?
• How are these myometrial conditions distinguished from one another and from other uterine factors?

Key concepts

• Benign smooth-muscle tumour (leiomyoma)
• Submucosal, intramural, and subserosal location
• Cavity distortion
• Adenomyosis and the junctional zone
• Endometrial receptivity
• Oestrogen and progesterone responsiveness
• Abnormal uterine bleeding

Mechanisms

Fibroids are clonal smooth-muscle tumours whose growth is influenced by oestrogen and progesterone. Their effect on fertility depends largely on location: submucosal fibroids and intramural fibroids that distort the endometrial cavity are most consistently associated with impaired implantation and pregnancy loss, plausibly through mechanical distortion, altered blood flow, and a disturbed implantation environment, whereas subserosal fibroids generally have little effect. Adenomyosis involves endometrial tissue within the myometrium with thickening and disruption of the junctional zone; proposed mechanisms for its association with subfertility include impaired uterine peristalsis, altered endometrial receptivity, and an inflammatory environment (Stewart et al., 2016; Zhai et al., 2020).

Clinical relevance

Fibroids and adenomyosis are common and are considered in the uterine evaluation of subfertile women, particularly when the cavity is distorted or symptoms such as heavy bleeding are present. This entry explains the link between these conditions and fertility for educational orientation; whether a lesion warrants intervention is a clinical decision guided by current evidence and not addressed prescriptively here.

Epidemiology

Uterine fibroids are very common, present in a large proportion of reproductive-age women by later reproductive years and showing higher prevalence and earlier onset among women of African ancestry; many are asymptomatic and do not affect fertility (Stewart et al., 2016). Adenomyosis prevalence estimates vary widely with diagnostic criteria and imaging, and it frequently coexists with fibroids and endometriosis (Zhai et al., 2020).

History

Fibroids have been described since antiquity and were characterised pathologically as benign smooth-muscle tumours in the nineteenth century. Adenomyosis was historically conflated with endometriosis until the conditions were separated, and its non-invasive recognition advanced with magnetic resonance imaging and high-resolution ultrasound that visualise the junctional zone, as reviewed by Zhai and colleagues.

Debates

Do intramural fibroids that do not distort the cavity affect fertility?

Submucosal and cavity-distorting fibroids are widely accepted to impair fertility, but whether non-distorting intramural fibroids meaningfully reduce fecundity, and whether their removal helps, remains uncertain and debated in the literature.

Seminal works

• stewart-2016
• stewart-2001
• zhai-2020

Frequently asked questions

Which fibroids are most likely to affect fertility?

Submucosal fibroids and intramural fibroids that distort the endometrial cavity are the ones most consistently linked to impaired implantation, whereas subserosal fibroids that do not affect the cavity generally have little impact.

How might adenomyosis reduce fertility?

Proposed mechanisms include disruption of the myometrial junctional zone and uterine peristalsis, altered endometrial receptivity, and an inflammatory environment; estimates of its effect vary because diagnosis depends on imaging criteria.