Matrix metalloproteinase and tissue inhibitors of metalloproteinases gene polymorphisms in disorders that influence fertility and pregnancy complications: A systematic review and meta-analysis

MMP-8 in Periodontal Sites of Postpartum and without-Any-Pregnancy Women

The hypothesis that physiological changes in women can affect periodontal tissues is the subject of this study, and inflammatory markers such as matrix metalloproteinase-8 can measure susceptibility to inflammation. The study aimed to analyze MMP-8 levels in periodontal sites of postpartum women and women without a history of pregnancy, comparing health parameters and periodontal disease. This is a case-control study with 40 participants, 20 cases (women in the postpartum period) and 20 controls (women without any pregnancy), who underwent clinical periodontal examination and the collection of crevicular gingival fluid. The ELISA test was used to detect MMP-8 levels. Postpartum women had worse periodontal parameters, such as bleeding index on probing, number of sites with CAL ≥ 3, and fewer teeth present. In the group of women without a history of pregnancy, a significantly lower MMP-8 level was observed in healthy sites and a higher one was observed in periodontal pockets (p < 0.01). In contrast, in postpartum women, MMP-8 levels were elevated in both healthy sites and periodontal pockets (p > 0.01). The MMP-8 levels in gingival fluid appear to be related to periodontal clinical parameters and may be a possible marker of enzymatic changes involved in periodontal tissue destruction in postpartum women.

hUMSCs Restore Uterine Function by Inhibiting Endometrial Fibrosis via Regulation of the MMP-9/TIMP-1 Ratio in CDDP-Induced Injury Rats

The fertility of females of childbearing age who are cured of cancer by chemotherapy is gradually declining globally. As a broad-spectrum chemotherapy drug in clinic, the damage of cisplatin (CDDP) to female reproductive function cannot be ignored. At present, the study of CDDP damage to the uterus is not sufficient, and the exact mechanism needs to be further explored. Therefore, we conducted this research to determine whether uterine injury in CDDP-induced injury rats might be improved by human umbilical cord mesenchymal stem cells (hUMSCs) and to further explore the precise mechanism. The rat model of CDDP-induced injury was established by intraperitoneal injection of CDDP, and hUMSCs were injected into the tail vein 7 days later. In vivo, uterine function in CDDP-induced injury rats was affected after hUMSC transplantation. In vitro, the specific mechanism was further explored from the cell and protein levels. Overall, the specific reason of CDDP-induced uterine dysfunction in rats was endometrial fibrosis, which was significantly improved after hUMSC transplantation. Further investigation of the mechanism found that hUMSCs could regulate the ratio of matrix metalloproteinase-9 (MMP-9)/tissue inhibitor of metalloproteinase-1 (TIMP-1) in endometrial stromal cells (EnSCs) after CDDP injury.

Effects of TIMP1 rs4898 Gene Polymorphism on Early-Onset Preeclampsia Development and Placenta Weight

Introduction: Some evidence indicates that the improper trophoblast invasion of maternal spiral arteries could be caused by an imbalance between matrix metalloproteinases (MMPs) and tissue inhibitors of metalloproteinases (TIMPs), leading to preeclampsia (PE) development. This study aimed to assess the potential role of MMP1, MMP9, TIMP1 and TIMP2 gene polymorphisms in the pathogenesis of PE. Materials and methods: A total of 308 Polish women, 115 preeclamptic (55 with early-onset preeclampsia [EOPE], 60 with late-onset preeclampsia [LOPE]) and 193 healthy pregnant women, all of Caucasian origin, were recruited to the study. PE was diagnosed following the ACOG criteria. The polymorphic variants of the MMP-TIMP pathway (MMP1 rs1799750, MMP9 rs17576, MMP9 rs17577, TIMP1 rs4898, TIMP2 rs2277698, TIMP2 rs55743137) were genotyped by polymerase chain reaction and restriction fragment length polymorphism. Results: Analyzing all SNPs in the MMP-TIMP pathway, no significant differences in allele frequencies between preeclamptic women and controls were observed. However, comparing the EOPE and LOPE groups with each other, we observed a statistically significant difference between them for the TIMP1 rs4898 variant. In the whole group of 308 women, the mean placenta weight was the lowest in carriers of the rs4898 CC genotype. Post hoc analysis revealed significant differences between CC-CT (p = 0.0209) and CC-TT (p = 0.0469). Additionally, during allele analysis, a statistically significant difference in the mean placenta weight (for C allele 529.32 ± 157.11 g, for T allele 560.24 ± 162.24 g, p = 0.021) was also observed. Conclusion: Our findings suggest a relationship between TIMP1 rs4898 (372T > C) polymorphism and increased risk of early-onset preeclampsia in a population of pregnant Polish women. Our data suggest that the TIMP1 rs4898 C allele might be associated with increased risk for early-onset, but not for late-onset preeclampsia. To evaluate the role of the TIMP1 polymorphic variants in the etiopathology of preeclampsia, further studies with a larger sample size are needed.

The genetic risk factors for pregnancy-induced hypertension: Evidence from genetic polymorphisms

Pregnancy-induced hypertension (PIH) is a multifactorial and severe pregnancy complication including preeclampsia/eclampsia, gestational hypertension, chronic (pre-existing) hypertension, and preeclampsia/eclampsia variants superimposed on chronic hypertension. PIH-induced maternal mortality accounts for approximately 9% of all maternal deaths over the world. A large number of case-control studies have established the importance of various genetic factors in the occurrence and development of PIH. In this narrative review, we summarized the genetic risk factors involved in the renin-angiotensin system, endothelin system, inflammatory factors, oxidative stress, and other functional networks, with the aim of sorting out the genetic factors that may play a potential role in PIH and providing new ideas to elucidate the pathogenesis of PIH.

Association of MMP-2, MMP-3, and MMP-9 Polymorphisms with Susceptibility to Recurrent Pregnancy Loss

Genetic causes that contribute to recurrent pregnancy loss (RPL) are not fully understood. The aim of this study was to evaluate the association of five polymorphisms at MMP-2, MMP-3, and MMP-9 genes with risk of RPL. Methods: The study comprised 250 women with RPL and 250 healthy controls. The MMP-2 (rs243865, rs2285053), MMP-3 (rs35068180), and MMP 9 (rs3918242, rs17576) polymorphisms were genotyped by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) assay. Results: A significant association was found between MMP-3 rs35068180 polymorphism and RPL risk. There was no significant association between RPL and polymorphisms at MMP-2 (rs243865, rs2285053) and MMP 9 (rs3918242, rs17576) genes. Conclusion: MMP-3 rs35068180 polymorphism may modulate RPL risk in Iranian women. There is no evidence to suggest that MMP-2 (rs243865, rs2285053) and MMP 9 (rs3918242, rs17576) polymorphisms are associated with RPL risk.

Correlation of TP53 (rs1625895), TP73 (rs3765730), MMP9 (rs17576), and MTHFR (rs868014) polymorphisms with low ovarian reserve

OBJECTIVE

To investigate the influence of the Single Nucleotide Polymorphisms (SNPs) TP53 rs1625895, TP73 rs3765730, MMP9 rs17576, and MTHFR rs868014 on ovarian reserve (OR) in infertile patients.

STUDY DESIGN

A prospective cross-sectional study was carried out in 145 infertile women. The patients were divided into two groups according to ovarian reserve, characterized by association between AMH levels and AFC:After patient distribution, both groups were compared (LOR X NOR) regarding the genotypes of the SNPs TP53 T/C rs1625895, TP73 G/A rs3765730, MMP9 Gln/Arg rs17576, and MTHFR A/G rs868014.

RESULT(S)

The frequency of the TP53-T/T genotype was greater in the LOR and the TP53-C/C genotype was more frequent in patients with NOR. This association was confirmed by the frequency of alleles, where the presence of the T allele was significantly higher in patients who exhibited LOR (P = 0.0003). The frequency of the TP73-G/G genotype and of the G allele was higher in the LOR group (P = 0.01). Considering the MMP9 gene, the frequency of the Gln/Gln genotype was higher in the LOR group. However, the Gln/Arg genotype and the Arg allele prevailed in the NOR group (P = 0.006). The frequency of the MTHFR-A/A genotype was higher in the LOR group, whereas that of the MTHFR-GG genotype was higher in the NOR group. The presence of allele A was significantly higher in the LOR group (P = 0.002). The regression analysis shows that patients who present the TP53-T/T, TP73-G/G, MMP9-Gln/Gln, and MTHFR-A/A genotypes are 3.6X, 3.1X, 3.2X, and 3.7X more likely of having LOR, respectively. In addition, the association of the TP53/TT + TP73/GG genotypes increased the chance of women being included in the LOR group in 5.7-fold.

CONCLUSION(S)

The genotypes TP53-T/T, TP73-G/G, MMP9-Gln/Gln, and MTHFR-A/A increase the chance of women to exhibit LOR. These polymorphisms could be useful as genetic markers of low ovarian reserve in infertile patients.

Identification of endometriosis-associated genes and pathways based on bioinformatic analysis

Endometriosis is associated with dysmenorrhea, chronic pelvic pain, and infertility. The specific mechanism of endometriosis remains unclear. The aim of this study was to apply a bioinformatics approach to reveal related pathways or genes involved in the development of endometriosis.The gene expression profiles of GSE25628, GSE5108, and GSE7305 were downloaded from the gene expression omnibus (GEO) database. Differentially expressed gene (DEG) analysis was performed using GEO2R. The database for annotation, visualization, and integrated discovery (DAVID) was utilized to analyze the functional enrichment, gene ontology (GO) and kyoto encyclopedia of genes and genomes (KEGG) pathway of the differentially expressed genes. A protein-protein interaction (PPI) network was constructed and module analysis was performed using search tool for the retrieval of interacting genes and cytoscape.A total of 119 common differentially expressed genes were extracted, consisting of 51 downregulated genes and 68 upregulated genes. The enriched functions and pathways of the DEGs and hub genes include DNA strand separation, cellular proliferation, degradation of the extracellular matrix, encoding of smooth muscle myosin as a major contractile protein, exiting the proliferative cycle and entering quiescence, growth regulation, and implication in a wide variety of biological processes.A bioinformatics approach combined with cell experiments in this study revealed that identifying DEGs and hub genes leads to better understanding of the molecular mechanisms underlying the progression of endometriosis, and efficient biomarkers underlying this pathway need to be further investigated.

Changes in gene expression of cervical collagens, metalloproteinases, and tissue inhibitors of metalloproteinases after partial cervical excision-induced preterm labor in mice

We investigated changes in gene expression of cervical collagens, matrix metalloproteinases (MMPs), and tissue inhibitors of metalloproteinases (TIMPs) during pre-gestational uterine cervical excision and/or inflammation-induced preterm labor in mice. Forty sexually mature female mice were uniformly divided into four groups: sham, cervical excision, lipopolysaccharide (LPS) injection, and cervical excision plus LPS injection. Partial cervical tissue excision was performed at five weeks of age before mating. LPS was injected into the lower right uterine horn near the cervix on gestational day 16. Mice were sacrificed immediately postpartum. Uterine cervices were collected and subjected to quantitative real-time PCR. Col4α1 and Col5α1 expression increased significantly in the cervical excision plus LPS injection group compared to the sham group (p < 0.01 and p = 0.024, respectively). MMP-14 expression levels increased in the cervical excision plus LPS injection group compared to the sham group (p < 0.01). TIMP-1 expression was not significantly decreased in this group. Increased expression levels of Col4α1, Col5α1, and MMP-14 were associated with cervical excision plus inflammation-induced preterm labor. Thus, pre-gestational cervical remodeling through specific collagen metabolism and MMP activation may involve the pathogenesis of spontaneous preterm labor.

The Roles of Matrix Metalloproteinases and Their Inhibitors in Human Diseases

Matrix metalloproteinases (MMPs) are a family of zinc-dependent extracellular matrix (ECM) remodeling endopeptidases that have the capacity to degrade almost every component of the ECM. The degradation of the ECM is of great importance, since it is related to embryonic development and angiogenesis. It is also involved in cell repair and the remodeling of tissues. When the expression of MMPs is altered, it can generate the abnormal degradation of the ECM. This is the initial cause of the development of chronic degenerative diseases and vascular complications generated by diabetes. In addition, this process has an association with neurodegeneration and cancer progression. Within the ECM, the tissue inhibitors of MMPs (TIMPs) inhibit the proteolytic activity of MMPs. TIMPs are important regulators of ECM turnover, tissue remodeling, and cellular behavior. Therefore, TIMPs (similar to MMPs) modulate angiogenesis, cell proliferation, and apoptosis. An interruption in the balance between MMPs and TIMPs has been implicated in the pathophysiology and progression of several diseases. This review focuses on the participation of both MMPs (e.g., MMP-2 and MMP-9) and TIMPs (e.g., TIMP-1 and TIMP-3) in physiological processes and on how their abnormal regulation is associated with human diseases. The inclusion of current strategies and mechanisms of MMP inhibition in the development of new therapies targeting MMPs was also considered.

The regulation of trophoblast invasion and decidual reaction by matrix metalloproteinase-2, metalloproteinase-7, and metalloproteinase-9 expressions in the rat endometrium

PURPOSE

We aimed to evaluate how matrix metalloproteinases (MMPs) regulate the trophoblast invasion and placentation.

METHODS

Female rats were divided into the estrous cycle and early pregnancy day groups. Obtained uterine tissues and implantation sites were processed for immunofluorescence and real-time PCR examinations.

RESULTS

The mRNA expression of MMP-7 was higher than MMP-2 and MMP-9. Immunofluorescence findings confirmed that MMP-2, MMP-7, and MMP-9 were localized in the endometrial stroma, while MMP-7 was high in glandular and lining epithelial cells throughout the entire estrous cycle. However, their immunolocalizations and mRNA expressions were dramatically changed with the early pregnancy days. The MMP-7 reached very strong immunostaining in the giant trophoblast cells (GTCs), and the cytoplasm of mature and differentiating decidual cells, whereas MMP-2 and MMP-9 were mostly seen in the primary decidual zone (PDZ), GTCs, and the endothelium of blood vessels.

CONCLUSIONS

All three MMPs seemed likely to be a key mediator of trophoblast invasion into the decidual region as well as angiogenesis during the placentation process. Due to the strong and wide expression of MMP-7 in the mature decidua, it could be suggested that MMP-7 is important for decidual ECM remodeling and it might be used as a new marker of decidual reaction.

Vascular mechanisms and molecular targets in hypertensive pregnancy and preeclampsia

Preeclampsia is a major complication of pregnancy manifested as hypertension and often intrauterine growth restriction, but the underlying pathophysiological mechanisms are unclear. Predisposing genetic and environmental factors cause placental maladaptations leading to defective placentation, apoptosis of invasive cytotrophoblasts, inadequate expansive remodeling of the spiral arteries, reduced uteroplacental perfusion pressure, and placental ischemia. Placental ischemia promotes the release of bioactive factors into the maternal circulation, causing an imbalance between antiangiogenic soluble fms-like tyrosine kinase-1 and soluble endoglin and proangiogenic vascular endothelial growth factor, placental growth factor, and transforming growth factor-β. Placental ischemia also stimulates the release of proinflammatory cytokines, hypoxia-inducible factor, reactive oxygen species, and angiotensin type 1 receptor agonistic autoantibodies. These circulating factors target the vascular endothelium, causing generalized endotheliosis in systemic, renal, cerebral, and hepatic vessels, leading to decreases in endothelium-derived vasodilators such as nitric oxide, prostacyclin, and hyperpolarization factor and increases in vasoconstrictors such as endothelin-1 and thromboxane A₂. The bioactive factors also target vascular smooth muscle and enhance the mechanisms of vascular contraction, including cytosolic Ca²⁺, protein kinase C, and Rho-kinase. The bioactive factors could also target matrix metalloproteinases and the extracellular matrix, causing inadequate vascular remodeling, increased arterial stiffening, and further increases in vascular resistance and hypertension. As therapeutic options are limited, understanding the underlying vascular mechanisms and molecular targets should help design new tools for the detection and management of hypertension in pregnancy and preeclampsia.

Expression of Matrix Metalloproteinase-9 and Tissue Inhibitor of Metalloproteinase-1 in Endometriosis Menstrual Blood

Endometriosis is a gynecological disease characterized by the presence of endometrial-like tissue outside the uterine cavity. Remodeling of the extracellular matrix (ECM) is a prerequisite for tissue implantation. The presence of matrix metalloproteinase (MMP) and its inhibitor, tissue inhibitor of metalloproteinase-1 (TIMP-1), in shed endometrium cells has a significant role in ECM degradation. A case–control study was performed to find other diagnostic markers using menstrual blood. We examined a sample of 68 women who visited the gynecology clinic in Dr Hasan Sadikin General Hospital, 40% of whom were confirmed to have endometriosis, and the rest tested negative by histopathological examination. All endometriotic cases presented MMP-9 and TIMP-1 expression with different cell distribution. MMP-9 expression in endometriosis patients was increased compared to the controls (p = 0.002). Expression of MMP-9 in >80% of endometrial cells was associated with a higher risk for endometriosis (OR 4.44 95% CI 1.31 to 15.56) compared to MMP-9 expression in 50%–80% of cells. TIMP-1 cell expression in women with endometriosis was lower than in the control group (p = 0.030). Subjects with TIMP-1 expression in 20%–50% of endometrial cells had a higher risk for endometriosis (OR 4.5, 95%CI 1.21–17.42) compared those with TIMP-1 expression in 50%–80% of cells. These expressions levels can be useful to predict endometriosis.

Expression of Matrix Metalloproteinases and Their Inhibitors in Endometrium: High Levels in Endometriotic Lesions

Endometriosis is a condition defined as presence of endometrium outside of the uterine cavity. These endometrial cells are able to attach and invade the peritoneum or ovary, thus forming respectively the deep infiltrating endometriosis (DIE) and the ovarian endometrioma (OMA), the ectopic lesions feature of this pathology. Endometriotic cells display high invasiveness and share some features of malignancy with cancer cells. Indeed, the tissue remodeling underlining lesion formation is achieved by matrix metalloproteinases (MMPs) and their inhibitors. Therefore, these molecules are believed to play a key role in development and pathogenesis of endometriosis. This study investigated the molecular profile of metalloproteinases and their inhibitors in healthy (n = 15) and eutopic endometrium (n = 19) in OMA (n = 10) and DIE (n = 9); moreover, we firstly validated the most reliable housekeeping genes allowing accurate gene expression analysis in these tissues. Gene expression, Western blot, and immunofluorescence analysis of MMP2, MMP3, and MMP10 and their tissue inhibitors TIMP1 and TIMP2 demonstrated that these enzymes are finely tuned in these tissues. In OMA lesions, all the investigated MMPs and their inhibitors were significantly increased, while DIE expressed high levels of MMP3. Finally, in vitro TNFα treatment induced a significant upregulation of MMP3, MMP10, and TIMP2 in both healthy and eutopic endometrial stromal cells. This study, shedding light on MMP and TIMP expression in endometriosis, confirms that these molecules are altered both in eutopic endometrium and endometriotic lesions. Although further studies are needed, these data may help in understanding the molecular mechanisms involved in the extracellular matrix remodeling, a crucial process for the endometrial physiology.

Cross-disorder analysis of endometriosis and its comorbid diseases reveals shared genes and molecular pathways and proposes putative biomarkers of endometriosis

RESEARCH QUESTION

Women with endometriosis are considered to be at higher risk of several chronic diseases, such as autoimmune disorders, gynaecological cancers, asthma/atopic diseases and cardiovascular and inflammatory bowel diseases. Could the study of endometriosis-associated comorbidities help to identify potential biomarkers and target pathways of endometriosis?

DESIGN

A systematic review was performed to identify all possible endometriosis-associated comorbid conditions. Next, this list of disorders was coded into MeSH terms, and the gene expression profiles were downloaded from the Phenopedia database and subsequently analysed following a systems biology approach.

RESULTS

The results identified a group of 127 candidate genes that were recurrently expressed in endometriosis and its closest comorbidities and that were defined as 'endometriosis sibling disorders' (ESD). The enrichment analysis showed that these candidate genes are principally involved in immune and drug responses, hormone metabolism and cell proliferation, which are well-known hallmarks of endometriosis. The expression of ESD genes was then validated on independent sample cohorts (n = 207 samples), in which the involvement of 16 genes (AGTR1, BDNF, C3, CCL2, CD40, CYP17A1, ESR1, IGF1, IGF2, IL10, MMP1, MMP7, MMP9, PGR, SERPINE1 and TIMP2) in endometriosis was confirmed. Several of these genes harbour polymorphisms that associate to either endometriosis or its comorbid conditions.

CONCLUSIONS

The study results highlight the molecular processes underlying the aetiopathogenesis of endometriosis and its comorbid conditions, and identify putative endometriosis biomarkers.

Granulocyte macrophage colony stimulating factor (GM-CSF), the critical intermediate of inflammation-induced fetal membrane weakening, primarily exerts its weakening effect on the choriodecidua rather than the amnion

INTRODUCTION

We have previously demonstrated two associations of PPROM, (1) inflammation/infection (modeled by tumor necrosis factor (TNF)) and (2) decidual bleeding (modeled by thrombin), both decrease fetal membrane (FM) rupture strength in-vitro. Furthermore, Granulocyte-Macrophage-Colony-Stimulating-Factor (GM-CSF) induced by both TNF and thrombin is a critical intermediate, necessary and sufficient for weakening by either agent. The amnion is the strength component of FM and must weaken for FM to rupture. It is unclear whether GM-CSF weakens amnion (AM) directly, or initially targets choriodecidua (CD) which secondarily releases agents to act on amnion.

METHODS

Full thickness FM fragments were treated with/without GM-CSF. Some were preincubated with alpha-lipoic acid (LA), a known inhibitor of FM weakening. The FM fragments were then strength-tested. Separately, FM fragments were initially separated to AM and CD. AM fragments were cultured with Medium ± GM-CSF and then strength-tested. In other experiments, CD fragments were cultured with Medium, GM-CSF, LA, or LA + GM-CSF. Conditioned medium from each group was then incubated with AM. AM was then strength-tested. Matrix Metalloproteinases (MMPs) and Tissue Inhibitors of Matrix Metalloproteinases (TIMPs) were analyzed by Mutiplex Elisa.

RESULTS

GM-CSF weakened intact FM which was blocked by LA. GM-CSF did not weaken isolated AM. However, GM-CSF conditioned CD media weakened AM and this weakening was inhibited by LA. GM-CSF treatment of CD increased MMPs 2, 9, and 10, and decreased TIMPs 1-3. LA reversed these effects.

CONCLUSIONS

GM-CSF does not weaken amnion directly; GM-CSF acts on CD to increase proteases and decrease anti-proteases which secondarily weaken the amnion.

Role of proteases in dysfunctional placental vascular remodelling in preeclampsia

Preeclampsia is a syndrome characterised by vascular dysfunction, impaired angiogenesis, and hypertension during pregnancy. Even when the precise pathophysiology of preeclampsia remains elusive, impaired vascular remodelling and placental angiogenesis in the placental villi and defective trophoblast invasion of the uterus are proposed as crucial mechanisms in this syndrome. Reduced trophoblast invasion leads to reduced uteroplacental blood flow and oxygen availability and increased oxidative stress. These phenomena trigger the release of soluble factors into the maternal and foetoplacental circulation that are responsible of the clinical features of preeclampsia. New blood vessels generation as well as vascular remodelling are mechanisms that require expression and activity of different proteases, including matrix metalloproteases, a-disintegrin and metalloproteases, and a-disintegrin and metalloprotease with thrombospondin motifs. These proteases exert proteolysis of the extracellular matrix. Additionally, cathepsins, a family of proteolytic enzymes, are primarily located in lysosomes but are also released by cells to the extracellular space. This review focuses on the role that these proteases play in the regulation of the uterine trophoblast invasion and the placental vascular remodelling associated with preeclampsia.

Urocortin Expression in Endometriosis: A Systematic Review

Urocortin (UCN) is a neuropeptide that belongs to the corticotrophin-releasing hormone family and is expressed by eutopic and ectopic human endometria. The past years, this expression has been thoroughly investigated in the field of endometriosis. The objective of this systematic review is to accumulate current evidence related to the expression of UCN in tissue and blood samples of patients suffering from endometriosis. Literature search was designed accord- ing to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and primarily conducted using the Medline (1966-2018), Scopus (2004-2018), EMBASE (1947-2018) and Clinicaltrials.gov (2008- 2018) databases, along with the reference lists of electronically retrieved full-text papers. Overall, eight studies were retrieved. Current evidence suggests that the expression of UCN is increased in patients with ovarian endometriomas and that its levels may correlate with the severity of the disease. The diagnostic efficacy of UCN1 plasma levels was evaluated in three studies. Two of them suggested that the sensitivity and specificity of the method may reach, and even exceed, 80%. However, the wide variation in outcome reporting and outcome reporting measures in endome- triosis among the included studies precludes meta-analysis of available data. Therefore, although UCN seems to be a promising biomarker for the identification and follow-up of patients that suffer from endometriosis, more studies are needed to reach firm conclusions with respect to its predictive accuracy.