Abstract
STUDY QUESTIONCan markers of human endometrial hypoxia be detected at menstruation in vivo?SUMMARY ANSWEROur in vivo data support the presence of hypoxia in menstrual endometrium of women during physiological menstruation.WHAT IS KNOWN ALREADYCurrent evidence from animal models and human in vitro studies suggests endometrial hypoxia is present at menstruation and drives endometrial repair post menses. However, detection of human endometrial hypoxia in vivo remains elusive.STUDY DESIGN, SIZE, DURATIONWe performed a prospective case study of 16 women with normal menstrual bleeding.PARTICIPANTS/MATERIALS, SETTING, METHODSReproductively aged female participants with a regular menstrual cycle underwent objective measurement of their menstrual blood loss using the alkaline haematin method to confirm a loss of <80 ml per cycle. Exclusion criteria were exogenous hormone use, an intrauterine device, endometriosis or fibroids >3 cm. Participants attended for two MRI scans; during days 1–3 of menstruation and the early/mid-secretory phase of their cycle. The MRI protocol included dynamic contrast-enhanced MRI and T2* quantification. At each visit, an endometrial sample was also collected and hypoxia-regulated repair factor mRNA levels (ADM, VEGFA, CXCR4) were quantified by RT-qPCR.MAIN RESULTS AND THE ROLE OF CHANCEWomen had reduced T2* during menstrual scans versus non-menstrual scans (P = 0.005), consistent with menstrual hypoxia. Plasma flow (Fp) was increased at menstruation compared to the non-menstrual phase (P = 0.0005). Laboratory findings revealed increased ADM, VEGF-A and CXCR4 at menstruation on examination of paired endometrial biopsies from the menstrual and non-menstrual phase (P = 0.008; P = 0.03; P = 0.009). There was a significant correlation between T2* and these ex vivo hypoxic markers (P < 0.05).LIMITATIONS, REASONS FOR CAUTIONThis study examined the in vivo detection of endometrial hypoxic markers at specific timepoints in the menstrual cycle in women with a menstrual blood loss <80 ml/cycle and without significant uterine structural abnormalities. Further research is required to determine the presence of endometrial hypoxia in those experiencing abnormal uterine bleeding with and without fibroids/adenomyosis.WIDER IMPLICATIONS OF THE FINDINGSHeavy menstrual bleeding (HMB) is a common, debilitating condition. Understanding menstrual physiology may improve therapeutics. To our knowledge, this is the first in vivo data supporting the presence of menstrual hypoxia in the endometrium of women with normal menstrual bleeding. If aberrant in those with HMB, these non-invasive tests may aid diagnosis and facilitate personalized treatments for HMB.STUDY FUNDING/COMPETING INTEREST(S)This work was funded by Wellbeing of Women grant RG1820, Wellcome Trust Fellowship 209589/Z/17/Z and undertaken in the MRC Centre for Reproductive Health, funded by grants G1002033 and MR/N022556/1. H.O.D.C. has clinical research support for laboratory consumables and staff from Bayer AG and provides consultancy advice (but with no personal remuneration) for Bayer AG, PregLem SA, Gedeon Richter, Vifor Pharma UK Ltd, AbbVie Inc; Myovant Sciences GmbH. H.O.D.C. receives royalties from UpToDate for articles on abnormal uterine bleeding.TRIAL REGISTRATION NUMBERN/A.
Highlights
Heavy menstrual bleeding (HMB) affects 20–30% of pre-menopausal women causing decreases in physical, psychological, economic and social health (RCOG, 2011)
Endometrial T2* was significantly lower in the menstrual phase compared to the non-menstrual phase (P 1⁄4 0.005) consistent with the presence of endometrial hypoxia at menses (Fig. 2)
Hypoxia in the human menstrual endometrium phase compared to the non-menstrual phase (P < 0.001) (Fig. 3a)
Summary
Heavy menstrual bleeding (HMB) affects 20–30% of pre-menopausal women causing decreases in physical, psychological, economic and social health (RCOG, 2011). Progesterone levels decline in the late secretory phase of the menstrual cycle due to corpus luteal regression. This causes an influx of inflammatory mediators to the local endometrial environment, including potent vasoconstrictors, e.g. prostaglandin-F2a and endothelin-1 (Smith et al, 1981; Marsh et al, 1997). This ‘injury’ leads to bleeding and shedding of the functional endometrial layer during menstruation. The endometrium undergoes re-epithelialization and stromal expansion in an efficient ‘repair’ phase to maintain function (i.e. receptivity) in the subsequent cycle (Critchley et al, 2020)
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