Uterine Fibroids Causing Preterm Birth: A New Pathophysiological Hypothesis on the Role of Fibroid Necrosis and Inflammation.

According to recent studies and observations in clinical practice, uterine fibroids increase the risk of preterm birth. There are several theories on the pathogenesis of preterm birth in the presence of fibroids. One theory proclaims that fibroid necrosis leads to preterm birth, though pathophysiological mechanisms have not been described. Necrotic tissue secretes specific cytokines and proteins and we suggest these to be comparable to the inflammatory response leading to spontaneous preterm birth. We hypothesize that fibroid necrosis could induce preterm parturition through a similar inflammatory response. This new hypothesis generates novel perspectives for future research and the development of preventative strategies for preterm birth. Moreover, we emphasize the importance of the recognition of fibroids and especially fibroid necrosis by clinicians during pregnancy.

The role of fibrosis in endometriosis: a systematic review.

BACKGROUND: Fibrosis is an important pathological feature of endometriotic lesions of all subtypes. Fibrosis is present in and around endometriotic lesions, and a central role in its development is played by myofibroblasts, which are cells derived mainly after epithelial-to-mesenchymal transition (EMT) and fibroblast-to-myofibroblast transdifferentiation (FMT). Transforming growth factor-ß (TGF-ß) has a key role in this myofibroblastic differentiation. Myofibroblasts deposit extracellular matrix (ECM) and have contracting abilities, leading to a stiff micro-environment. These aspects are hypothesized to be involved in the origin of endometriosis-associated pain. Additionally, similarities between endometriosis-related fibrosis and other fibrotic diseases, such as systemic sclerosis or lung fibrosis, indicate that targeting fibrosis could be a potential therapeutic strategy for non-hormonal therapy for endometriosis. OBJECTIVE AND RATIONALE: This review aims to summarize the current knowledge and to highlight the knowledge gaps about the role of fibrosis in endometriosis. A comprehensive literature overview about the role of fibrosis in endometriosis can improve the efficiency of fibrosis-oriented research in endometriosis. SEARCH METHODS: A systematic literature search was performed in three biomedical databases using search terms for 'endometriosis', 'fibrosis', 'myofibroblasts', 'collagen', and 'α-smooth muscle actin'. Original studies were included if they reported about fibrosis and endometriosis. Both preclinical in vitro and animal studies, as well as research concerning human subjects were included. OUTCOMES: Our search yielded 3441 results, of which 142 studies were included in this review. Most studies scored a high to moderate risk of bias according to the bias assessment tools. The studies were divided in three categories: human observational studies, experimental studies with human-derived material, and animal studies. The observational studies showed details about the histologic appearance of fibrosis in endometriosis and the co-occurrence of nerves and immune cells in lesions. The in vitro studies identified several pro-fibrotic pathways in relation to endometriosis. The animal studies mainly assessed the effect of potential therapeutic strategies to halt or regress fibrosis, for example targeting platelets or mast cells. WIDER IMPLICATIONS: This review shows the central role of fibrosis and its main cellular driver, the myofibroblast, in endometriosis. Platelets and TGF-ß have a pivotal role in pro-fibrotic signaling. The presence of nerves and neuropeptides is closely associated with fibrosis in endometriotic lesions, and is likely a cause of endometriosis-associated pain. The process of fibrotic development after EMT and FMT shares characteristics with other fibrotic diseases, so exploring similarities in endometriosis with known processes in diseases like systemic sclerosis, idiopathic pulmonary fibrosis or liver cirrhosis is relevant and a promising direction to explore new treatment strategies. The close relationship with nerves appears rather unique for endometriosis-related fibrosis and is not observed in other fibrotic diseases. REGISTRATION NUMBER: N/A.

Preterm birth and uterine fibroid necrosis: The clinical presentation illustrated in a case series.

OBJECTIVE: Uterine fibroids increase the risk of preterm birth. The current study highlights uterine fibroid necrosis as a possible cause of (extreme) preterm birth. STUDY DESIGN: Retrospective cohort study in one Dutch academic hospital. Cases were selected from the 526 participants of the MyoFert study (Netherlands Trial Register, NL7990), which included patients who presented between 2004 and 2018 and were between the age of 18 and 45 years at the time of diagnosis of uterine fibroids. Of these participants, 414 women became pregnant. A retrospective chart review of the first pregnancies was performed. The main outcomes were (imminent) preterm birth and signs of fibroid necrosis on ultrasound. In women with signs of fibroid necrosis, the following data were collected systematically: fibroid characteristics, clinical presentation, pregnancy outcome, and postpartum period. RESULTS: In total, 66 women had a preterm birth (16 %, 66/414), of which 25 pregnancies ended between 16 and <24 weeks (38 %, 25/66) and 41 pregnancies ended between 24 and <37 weeks of gestation (62 %, 41/66). Of all women with preterm birth and available ultrasound images, 15 % (7/48) had fibroid necrosis at the time of labour. These seven patients, supplemented with three patients with fibroid necrosis during their first pregnancy and at least one episode of imminent preterm birth, are described in more detail. In these ten patients, the fibroids increased substantially in size during the first and second trimester, leading to severe abdominal pain in all patients and hospital admission in seven patients. Ultrasound examination of the fibroids showed heterogenic changes and focal transonic areas in the fibroid, which are characteristics that indicate fibroid necrosis. In four patients, myomectomy was performed and necrosis was confirmed histologically. CONCLUSION: Fibroid necrosis during pregnancy is likely associated with (imminent) preterm birth. Clinicians are advised to structurally evaluate the myometrium in pregnancy, specifically in women presenting with abdominal pain in the second trimester.

The risk of preterm birth in women with uterine fibroids: A systematic review and meta-analysis.

BACKGROUND: Fibroids have been identified as a possible risk factor for preterm birth, however, the magnitude of this risk is unclear. Our objective was to determine the risk of total, spontaneous, and medically indicated preterm birth in women with fibroids. METHODS: A literature search was performed on 9 June 2021. We selected studies reporting on preterm birth in women with and without fibroids. Fibroids had to be diagnosed by routine ultrasound before or during pregnancy. Main outcomes were total preterm birth <37, <34, <32, and <28 weeks of gestation, and spontaneous and medically indicated preterm birth. Two authors independently performed study selection, data extraction and quality assessment. We performed quality assessment with the Newcastle-Ottawa scale. Meta-analyses were presented as Odds Ratios (ORs) with 95% Confidence Intervals (95%CIs). MAIN RESULTS: The search yielded 2078 unique articles of which 11 were included. Meta-analysis for preterm birth <37 weeks of gestation included 256,650 singleton deliveries: 12,309 with fibroids and 244,341 without fibroids. Women with fibroids had a higher rate of preterm birth (11.6% versus 9.0%; OR 1.66, 95%CI 1.29-2.14). Fibroids were also associated with preterm birth <34 (OR 1.88, 95%CI 1.34-2.65), <32 (OR 2.03, 95%CI 1.40-2.95) and <28 (OR 2.24, 95%CI 1.45-3.47) weeks of gestation. Data on type of preterm birth was limited: one study showed a significant association of fibroids with spontaneous preterm birth and another with indicated preterm birth. The main limitations of the included studies were the lack of correction for confounders, the risk of ascertainment bias due to possible underreporting of fibroids, and the substantial heterogeneity between studies. CONCLUSIONS: Our results suggest fibroids are associated with an increased risk of preterm birth, with a stronger risk at earlier gestational ages. We encourage further research to clarify the association between fibroids and preterm birth by systematic myometrial assessment in pregnancy. REGISTRATION: Prospero database [CRD42020186976].