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Endometrial thickness assessed by transvaginal ultrasound in transmasculine people taking testosterone compared with cisgender women

Open AccessPublished:June 21, 2022DOI:https://doi.org/10.1016/j.rbmo.2022.06.012

      Highlights

      • Endometrial thickness in trans masculine persons is lower compared to cis women
      • No endometrial abnormalities were detected by ultrasound in either group
      • Burdensome endometrial screening may not be necessary in trans masculine persons

      Abstract

      Research question

      What is the endometrial thickness of endometrium exposed to testosterone in transmasculine people compared with unexposed endometrium in cisgender women as determined by transvaginal ultrasound (TVU)?

      Design

      Single centre, cross-sectional cohort study conducted the Centre of Expertise on Gender Dysphoria in Amsterdam. Between 2013 and 2015, transmasculine people scheduled for gender affirming surgery (GAS) were included in this study after they provided informed consent. They were undergoing gender affirming hormone therapy (testosterone) for at least 1 year. Endometrial thickness (mm) was measured by TVU in transmasculine people, immediately before their GAS while under general anaesthesia. Cisgender control women from the general population underwent the exact same TVU measurements in an outpatient clinical setting on cycle days 2–5.

      Result

      Fifty-one transmasculine people and 77 controls were included. The mean duration of testosterone use was 30.2 months (SD 8.8). Endometrial thickness was significantly lower in transmasculine people compared with cisgender women: median 3.9 mm (interquartile range [IQR] 2.8–5.1) and 4.9 mm (IQR 4.0–6.3), respectively (P < 0.001), after correcting for confounding factor (current gonadotrophin releasing hormone agonist use).

      Conclusions

      Endometrial thickness in transmasculine people exposed to testosterone is significantly lower compared with cisgender women without testosterone exposure. These results suggest an absence of endometrial proliferation by exogenous testosterone.

      KEYWORDS

      Introduction

      Transgender individuals experience gender dysphoria. This refers to the discrepancy between a person's gender assigned at birth and their gender identity (
      • Coleman E.
      • Bockting W.
      • Botzer M.
      • Cohen-Kettenis P.
      • DeCuypere G.
      • Feldman J.
      • Fraser L.
      • Green J.
      • Knudson G.
      • Meyer W.J.
      • Monstrey S.
      • Adler R.K.
      • Brown G.R.
      • Devor A.H.
      • Ehrbar R.
      • Ettner R.
      • Eyler E.
      • Garofalo R.
      • Karasic D.H.
      • Lev A.I.
      • Mayer G.
      • Meyer-Bahlburg H.
      • Hall B.P.
      • Pfaefflin F.
      • Rachlin K.
      • Robinson B.
      • Schechter L.S.
      • Tangpricha V.
      • van Trotsenburg M.
      • Vitale A.
      • Winter S.
      • Whittle S.
      • Wylie K.R.
      • Zucker K.
      Standards of Care for the Health of Transsexual, Transgender, and Gender-Nonconforming People, Version 7.
      ). The term transmasculine people will be used throughout to describe individuals who were assigned female at birth but do not identify as female, including but not limited to transgender men, genderqueer and non-binary persons.
      To transition to a more masculine physique, most transmasculine people seek medical treatment in the form of gender affirming hormone treatment (GAHT) with testosterone, gender affirming surgery (GAS), i.e. mastectomy (
      • Wiepjes C.M.
      • Nota N.M.
      • de Blok C.J.M.
      • Klaver M.
      • de Vries A.L.C.
      • Wensing-Kruger S.A.
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      • Steensma T.D.
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      • Gooren L.J.G.
      • Kreukels B.P.C.
      • den Heijer M.
      The Amsterdam Cohort of Gender Dysphoria Study (1972-2015): Trends in Prevalence, Treatment, and Regrets.
      ), or both. In 2014, transgender laws in the Netherlands were abolished and transgender people were no longer obligated to be sterile to change their gender in official documents (Dutch civil law, article 1:28). Since then, fewer transmasculine people desire a hysterectomy as part of their transition and choose to retain their reproductive organs, either now or indefinitely (
      • Grimstad F.W.
      • Fowler K.G.
      • New E.P.
      • Ferrando C.A.
      • Pollard R.R.
      • Chapman G.
      • Gray M.
      • Gomez Lobo V.
      Ovarian Histopathology in Transmasculine Persons on Testosterone: A Multicenter Case Series.
      ). Combined with a reported worldwide increase in gender dysphoria (
      • Wiepjes C.M.
      • Nota N.M.
      • de Blok C.J.M.
      • Klaver M.
      • de Vries A.L.C.
      • Wensing-Kruger S.A.
      • de Jongh R.T.
      • Bouman M.B.
      • Steensma T.D.
      • Cohen-Kettenis P.
      • Gooren L.J.G.
      • Kreukels B.P.C.
      • den Heijer M.
      The Amsterdam Cohort of Gender Dysphoria Study (1972-2015): Trends in Prevalence, Treatment, and Regrets.
      ), this will result in the endometrium of more transmasculine people being exposed to testosterone over a longer period of time.
      Although testosterone therapy is generally considered safe, the question about risk of endometrial hyperplasia and endometrial cancer remains (
      • Allen N.E.
      • Key T.J.
      • Dossus L.
      • Rinaldi S.
      • Cust A.
      • Lukanova A.
      • Peeters P.H.
      • Onland-Moret N.C.
      • Lahmann P.H.
      • Berrino F.
      • Panico S.
      • Larrañaga N.
      • Pera G.
      • Tormo M.J.
      • Sánchez M.J.
      • Ramón Quirós J.
      • Ardanaz E.
      • Tjønneland A.
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      • Schulz M.
      • Boeing H.
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      • Palli D.
      • Overvad K.
      • Clavel-Chapelon F.
      • Boutron-Ruault M.C.
      • Bingham S.
      • Khaw K.T.
      • Bueno-de-Mesquita H.B.
      • Trichopoulou A.
      • Trichopoulos D.
      • Naska A.
      • Tumino R.
      • Riboli E.
      • Kaaks R.
      Endogenous sex hormones and endometrial cancer risk in women in the European Prospective Investigation into Cancer and Nutrition (EPIC).
      ;
      • de Blok C.J.M.
      • Dreijerink K.M.A.
      • den Heijer M.
      Cancer Risk in Transgender People.
      ). This is based on the following findings: first, in theory, the aromatization of testosterone to oestradiol may induce proliferation of the endometrium. Endometrial exposure to oestradiol, unopposed by progesterone, is a known risk factor for endometrial cancer (
      • Barry J.A.
      • Azizia M.M.
      • Hardiman P.J.
      Risk of endometrial, ovarian and breast cancer in women with polycystic ovary syndrome: a systematic review and meta-analysis.
      ;
      • Grimstad F.W.
      • Fowler K.G.
      • New E.P.
      • Ferrando C.A.
      • Pollard R.R.
      • Chapman G.
      • Gomez-Lobo V.
      • Gray M.
      Uterine pathology in transmasculine persons on testosterone: a retrospective multicenter case series.
      ). In cisgender (i.e. non transgender) women with anovulation, it is known that endometrial hyperplasia prevails in 41% (
      • Xue Z.
      • Li J.
      • Feng J.
      • Han H.
      • Zhao J.
      • Zhang J.
      • Han Y.
      • Wu X.
      • Zhang Y.
      Research Progress on the Mechanism Between Polycystic Ovary Syndrome and Abnormal Endometrium [Review].
      ). Studies indicate a two- to six-fold increased risk of endometrial cancer in women with polycystic ovary syndrome (PCOS), which often presents before menopause; however, absolute risk of endometrial cancer remains relatively low (
      • Teede H.J.
      • Misso M.L.
      • Costello M.F.
      • Dokras A.
      • Laven J.
      • Moran L.
      • Piltonen T.
      • Norman R.J.
      International evidencebased guideline for the assessment and management of polycystic ovary syndrome.
      ). Another study showed that women who had PCOS at reproductive age with a thick endometrium (>7 mm) had an 8.7% risk of having endometrial neoplasia (
      • Indhavivadhana S.
      • Rattanachaiyanont M.
      • Wongwananuruk T.
      • Techatraisak K.
      • Rayasawath N.
      • Dangrat C.
      Endometrial neoplasia in reproductive-aged Thai women with polycystic ovary syndrome.
      ). Second, testosterone has been shown to be involved in the regulation of sex hormone receptor expression in the endometrium and may, therefore, influence endometrial proliferation and differentiation (
      • Zang H.
      • Sahlin L.
      • Masironi B.
      • Hirschberg A.L.
      Effects of testosterone and estrogen treatment on the distribution of sex hormone receptors in the endometrium of postmenopausal women.
      ). Third, androgen receptors have also been detected in endometrial carcinomas (
      • Maia Jr., H.
      • Maltez A.
      • Fahel P.
      • Athayde C.
      • Coutinho E
      Detection of testosterone and estrogen receptors in the postmenopausal endometrium.
      ).
      Reassuringly, only one case of endometrial cancer (
      • Urban R.R.
      • Teng N.N.H.
      • Kapp D.S.
      Gynecologic malignancies in female-to-male transgender patients: the need of original gender surveillance.
      ) and one case of atypical endometrial hyperplasia, with small focus of adenocarcinoma (
      • Grynberg M.
      • Fanchin R.
      • Dubost G.
      • Colau J.C.
      • Bremont-Weil C.
      • Frydman R.
      • Ayoubi J.M.
      Histology of genital tract and breast tissue after long-term testosterone administration in a female-to-male transsexual population.
      ) in transmasculine people using GAHT, have previously been reported. In addition, multiple studies examining histology of removed uteri during GAS did not describe endometrial malignancy (
      • Futterweit W.
      • Deligdisch L.
      Histopathological effects of exogenously administered testosterone in 19 female to male transsexuals.
      ;
      • Miller N.
      • Bédard Y.C.
      • Cooter N.B.
      • Shaul D.L.
      Histological changes in the genital tract in transsexual women following androgen therapy.
      ;
      • Perrone A.M.
      • Cerpolini S.
      • Maria Salfi N.C.
      • Ceccarelli C.
      • De Giorgi L.B.
      • Formelli G.
      • Casadio P.
      • Ghi T.
      • Pelusi G.
      • Pelusi C.
      • Meriggiola M.C.
      Effect of long-term testosterone administration on the endometrium of female-to-male (FtM) transsexuals.
      ;
      • Grynberg M.
      • Fanchin R.
      • Dubost G.
      • Colau J.C.
      • Bremont-Weil C.
      • Frydman R.
      • Ayoubi J.M.
      Histology of genital tract and breast tissue after long-term testosterone administration in a female-to-male transsexual population.
      ;
      • Loverro G.
      • Resta L.
      • Dellino M.
      • Edoardo D.N.
      • Cascarano M.A.
      • Loverro M.
      • Mastrolia S.A.
      Uterine and ovarian changes during testosterone administration in young female-to-male transsexuals.
      ;
      • Grimstad F.W.
      • Fowler K.G.
      • New E.P.
      • Ferrando C.A.
      • Pollard R.R.
      • Chapman G.
      • Gomez-Lobo V.
      • Gray M.
      Uterine pathology in transmasculine persons on testosterone: a retrospective multicenter case series.
      ;
      • Khalifa M.A.
      • Toyama A.
      • Klein M.E.
      • Santiago V.
      Histologic Features of Hysterectomy Specimens From Female-Male Transgender Individuals.
      ;
      • Ralph O.
      • Shroff N.
      • Christopher N.
      • Ahmed A.
      • Berner A.
      • Barrett J.
      • Sandison A.
      • Ralph D.
      Response of endometrium to testosterone therapy in transmen and non-binary people undergoing hysterectomy.
      ;
      • Hawkins M.
      • Deutsch M.B.
      • Obedin-Maliver J.
      • Stark B.
      • Grubman J.
      • Jacoby A.
      • Jacoby V.L.
      Endometrial findings among transgender and gender nonbinary people using testosterone at the time of gender-affirming hysterectomy.
      ).
      The risk of (lifelong) GAHT on developing endometrial hyperplasia and cancer is not yet known; therefore, it is also unclear if a specific ultrasound strategy should be executed. In asymptomatic cisgender women, routine endometrial ultrasound screening is never recommended, not even in cisgender women with PCOS (
      • Yin W.
      • Falconer H.
      • Yin L.
      • Xu L.
      • Ye W.
      Association Between Polycystic Ovary Syndrome and Cancer Risk.
      ). The only advice on endometrial ultrasound screening relates to post-menopausal women. Here, screening is only recommended when a patient presents with post-menopausal vaginal blood loss. An endometrial biopsy is taken when the endometrial thickness exceeds 4 mm on transvaginal ultrasound (TVU) (
      ACOG
      ACOG Committee Opinion No. 734: The Role of Transvaginal Ultrasonography in Evaluating the Endometrium of Women With Postmenopausal Bleeding.
      ). The lack of scientific evidence has led to conflicting guidelines for endometrial screening in transmasculine people. The World Professional Association for Transgender Health Standards of Care guidelines do not make a recommendation (
      • Coleman E.
      • Bockting W.
      • Botzer M.
      • Cohen-Kettenis P.
      • DeCuypere G.
      • Feldman J.
      • Fraser L.
      • Green J.
      • Knudson G.
      • Meyer W.J.
      • Monstrey S.
      • Adler R.K.
      • Brown G.R.
      • Devor A.H.
      • Ehrbar R.
      • Ettner R.
      • Eyler E.
      • Garofalo R.
      • Karasic D.H.
      • Lev A.I.
      • Mayer G.
      • Meyer-Bahlburg H.
      • Hall B.P.
      • Pfaefflin F.
      • Rachlin K.
      • Robinson B.
      • Schechter L.S.
      • Tangpricha V.
      • van Trotsenburg M.
      • Vitale A.
      • Winter S.
      • Whittle S.
      • Wylie K.R.
      • Zucker K.
      Standards of Care for the Health of Transsexual, Transgender, and Gender-Nonconforming People, Version 7.
      ), US guidelines advise against asymptomatic screening (

      Deutsch, M.B., e. (June 2016). UCSF Transgender Care, Department of Family and Community Medicine, University of California San Francisco. Guidelines for the Primary and Gender-Affirming Care of Transgender and Gender Nonbinary People; 2nd edition. transcare.ucsf.edu/guidelines

      ) and Dutch guidelines advise a routine uterine ultrasound and potential endometrial biopsy every 5 years ().
      Endometrial thickness as shown on TVU in transmasculine people using testosterone is rarely described. To help bridge this knowledge gap, we report previously unpublished data of endometrial measurements from a study by
      • Caanen M.R.
      • Schouten N.E.
      • Kuijper E.A.M.
      • van Rijswijk J.
      • van den Berg M.H.
      • van Dulmen-den Broeder E.
      • Overbeek A.
      • van Leeuwen F.E.
      • van Trotsenburg M.
      • Lambalk C.B.
      Effects of long-term exogenous testosterone administration on ovarian morphology, determined by transvaginal (3D) ultrasound in female-to-male transsexuals.
      . The aim of the present study was to describe endometrial thickness of endometrium exposed to testosterone in transmasculine people compared with unexposed endometrium in cisgender women determined by transvaginal ultrasound (TVU).

      Materials and methods

      In the present study, the ultrasound characteristics of the endometrium in transmasculine people using GAHT, testosterone and cisgender female controls with endometrial thickness as our primary outcome measure were analysed. The TVU was conducted during a previous study that aimed to compare ovarian morphology between transgender men and cisgender female controls. In this prospective, observational case-control study (
      • Caanen M.R.
      • Schouten N.E.
      • Kuijper E.A.M.
      • van Rijswijk J.
      • van den Berg M.H.
      • van Dulmen-den Broeder E.
      • Overbeek A.
      • van Leeuwen F.E.
      • van Trotsenburg M.
      • Lambalk C.B.
      Effects of long-term exogenous testosterone administration on ovarian morphology, determined by transvaginal (3D) ultrasound in female-to-male transsexuals.
      ), further details on study design and cohort characteristics are reported.

      Study design

      This single centre, cross-sectional cohort study was carried out at the Centre of Expertise on Gender Dysphoria in Amsterdam, the Netherlands, between 2013 and 2015. This study was approved by the local Ethical Committee on 4 September 2014 (reference number: 2014.402), and written informed consent was obtained from all participants. The trial was registered in the Dutch National Trial Registry (trial registration number NTR4784).

      Participants

      All eligible transmasculine adults, treated with testosterone for at least 1 year and who were eligible for GAS, in this case, hysterectomy and bilateral salpingo-oophorectomy, were invited to participate in the study. Baseline characteristics included age, height, weight, medical history, medication, type of testosterone, duration of testosterone use, current or prior gonadotrophin releasing hormone agonist (GnRHa) use (cessation ≥1 year), menstrual status and lifestyle factors, i.e. smoking, alcohol and drug use were retrieved from medical records.
      Controls were obtained from the control group of the Dutch LATER-VEVO study (trial registration number NTR2922) (
      • Annelies Overbeek M.H.v.d.B.
      • Kremer Leontien C.M.
      • Heuvel-Eibrink Marry M.van den
      • Tissing Wim J.E.
      • Loonen Jacqueline J.
      • Versluys Birgitta
      • Bresters Dorine
      • Kaspers Gertjan J.L.
      • Lambalk Cornelis B.
      • Leeuwen Flora E.van
      • Dulmen-den Eline van
      • Broeder on behalf of the DCOG LATER-VEVO study group
      A nationwide study on reproductive function, ovarian reserve, and risk of premature menopause in female survivors of childhood cancer: design and methodological challenges.
      ), a large nationwide study on reproductive function, ovarian reserve and premature menopause in female childhood cancer survivors. All controls were cisgender female adults from the general population, recruited via general practitioners or approached via participating childhood cancer survivors. Eligibility criteria, detailed study characteristics and both types of controls have been previously described by
      • Annelies Overbeek M.H.v.d.B.
      • Kremer Leontien C.M.
      • Heuvel-Eibrink Marry M.van den
      • Tissing Wim J.E.
      • Loonen Jacqueline J.
      • Versluys Birgitta
      • Bresters Dorine
      • Kaspers Gertjan J.L.
      • Lambalk Cornelis B.
      • Leeuwen Flora E.van
      • Dulmen-den Eline van
      • Broeder on behalf of the DCOG LATER-VEVO study group
      A nationwide study on reproductive function, ovarian reserve, and risk of premature menopause in female survivors of childhood cancer: design and methodological challenges.
      . Baseline characteristics were retrieved from a large self-reported questionnaire.
      Participants were excluded in case of disorders of sexual development, endocrine pathology including polycystic ovary syndrome, excessive smoking, alcohol, drug abuse, or both, and the use of hormonal contraceptives.

      Gender affirming hormone treatment

      Following the European protocol (
      • Dekker M.J.
      • Wierckx K.
      • Van Caenegem E.
      • Klaver M.
      • Kreukels B.P.
      • Elaut E.
      • Fisher A.D.
      • van Trotsenburg M.A.
      • Schreiner T.
      • den Heijer M.
      • T'Sjoen G.
      A European Network for the Investigation of Gender Incongruence: Endocrine Part.
      ), GAHT in adults consists of transdermal testosterone administration: Androgel®, 25 or 50 mg, daily (Besins International, Belgium), Tostran® 40 mg, daily (ProStakan, Galashiels, Scotland), and intramuscular injection (Nebido®, 1 g, per 10–14 weeks) (Bayer, Leverkusen Germany); or Sustanon®, 250 mg per 2–4 weeks (Aspen Pharma Trading Limited, Dublin Ireland).
      Before testosterone treatment, adolescents may start with puberty suppression treatment with gonadotrophin-releasing hormone agonist (GnRHa) desensitization to prevent (further) development of secondary sex characteristics not fitting with the experienced gender identity. When transitioning from GnRHa to testosterone, GnRHa was continued for several months, sometimes even until undergoing GAS.
      In clinical practice, transmasculine people were advised to discontinue their GAHT before GAS for 2–6 weeks, to prevent a then assumed additional risk of blood clots during and after surgery.

      Transvaginal ultrasound

      Endometrial thickness (in mm) was measured by TVU in longitudinal, two-dimensional view using the HD11 XE ultrasound system with a three-dimensional transvaginal probe (3–9 MHz; EnVisor HD) (Philips Medical Systems, Eindhoven, the Netherlands) in both groups according to the same ultrasound protocol. The transmasculine people underwent TVU, carried out by two experienced research physicians, at the time of GAS while under general anaesthesia. Controls underwent the same TVU measurements in an outpatient clinical setting on cycle day 2–5 by several experienced sonographers. All images were evaluated by two blinded research team members. Endometrial thickness was determined by both researchers via a standardized protocol and an average of both measurements was used. If the endometrial thickness measurements reported by both team members were too far apart to determine a reliable average, a third person (supervisor) would repeat the measurement. During TVU, abnormalities of the endometrium and uterus were also documented.

      Statistical analysis

      SPSS version 20.0 (SPSS, Inc., Chicago, IL, USA) was used for all statistical analyses. Baseline characteristics and outcomes are reported as mean (SD), median (interquartile range) or number (percentages). Non-parametric Mann–Whitney U test was carried out when appropriate. Linear regression analyses were conducted to correct for possible confounders, current GnRHa use (yes/no), current progesterone use (yes/no), type of testosterone used, age and body mass index (BMI). A two-tailed P < 0.05 was considered significant.

      Results

      In total, 128 participants were included: 51 transmasculine people and 77 cisgender controls. Baseline characteristics are presented in Table 1. The transmasculine people were younger and had a higher BMI (P < 0.001 and P = 0.005, respectively). The mean duration of testosterone use was 30.2 months (SD 8.8). The most common type of testosterone administration was via intramuscular injection (65%), the other people used transdermal gel (35%). Forty-seven per cent of transmasculine people used GnRHa during their medical transition. Twenty-nine per cent were still using GnRHa at the time of participation in this study. Furthermore, 14% of participants were using a type of progesterone for cycle regulation or contraceptive needs. No data on menstrual status were available.
      Table 1BASELINE CHARACTERISTICS OF TRANSMASCULINE PEOPLE AND CISGENDER WOMEN
      CharacteristicsTransmasculine people (cases) (n = 51)Cisgender women (controls) (n = 77)P-value
      Age, years22.6 (19.3–26.3)34.0 (30.9–36.0)<0.001
      P-values for continuous variables non-parametric Mann–Whitney U test. BMI, body mass index; GnRHa, gonadotrophin releasing hormone agonist; TVU, transvaginal ultrasound; –, not applicable".
      BMI, kg/m223.5 (21.1–28.7)22.0 (20.8–23.5)0.005
      P-values for continuous variables non-parametric Mann–Whitney U test. BMI, body mass index; GnRHa, gonadotrophin releasing hormone agonist; TVU, transvaginal ultrasound; –, not applicable".
      Testosterone use, months30.2 (8.8)
      Type of testosterone
      Intramuscular33 (65%)
      Transdermal18 (35%)
      GnRHa use, ever24 (47%)
      GnRHa use, at time of TVU15 (29%)
      Progesterone7 (14%)
      Data are expressed in mean (SD), median (IQR) and numbers (%).
      a P-values for continuous variables non-parametric Mann–Whitney U test.BMI, body mass index; GnRHa, gonadotrophin releasing hormone agonist; TVU, transvaginal ultrasound; –, not applicable".
      Endometrial thickness in transmasculine people and cisgender controls are presented in Figure 1. Endometrial thickness was significantly lower in the transmasculine people with a median of 3.9 mm compared with 4.9 mm in the controls (P < 0.001). When conducting linear regression analyses, only current GnRHa use was identified as a confounding factor. Age, BMI, progesterone use and type of testosterone were not confounders. After correcting for current GnRHa use, this difference in endometrial thickness remained significant (P < 0.001).
      Figure 1
      Figure 1Endometrial thickness in transmasculine people (51 cases) and cisgender women (77 controls) assessed by transvaginal ultrasound. Box and Whisker plot shows median, interquartile range, maximum and minimum values and outliers. Median endometrial thickness was 3.9 mm (2.8–5.1) and 4.9 mm (4.0–6.3) in cases and controls, respectively. The crude P-value was <0.001 and the adjusted P-value in linear regression analyses (adjusted for confounding factor, current gonadotrophin releasing hormone agonist use) was <0.001.
      Abnormalities of the endometrium were not found in any of the participants. In five transmasculine people and in seven controls, the uterus was described as abnormal owing to the presence of fibroids.

      Discussion

      To the best of our knowledge, the present study is the first to describe endometrial thickness assessed by TVU in transmasculine people using GAHT compared with cisgender women. In our cohort, the endometrial thickness was significantly lower in transmasculine people compared with early follicular phase values in cisgender women even after correcting for confounding factor, current GnRHa use (3.9 mm versus 4.9 mm, P < 0.001).
      The findings of our study are in line with the limited research on TVU in transmasculine people undergoing GAHT. One observational study by
      • Mueller A.
      • Kiesewetter F.
      • Binder H.
      • Beckmann M.W.
      • Dittrich R.
      Long-Term Administration of Testosterone Undecanoate Every 3 Months for Testosterone Supplementation in Female-to-Male Transsexuals.
      described a significant reduction of endometrial thickness and no noticeable endometrial pathology on TVU in transmasculine people 1 year after starting GAHT. The endometrial thickness was 9.9 mm (SD 4.2) at baseline and 5.7 mm (SD 1.4) at 12 months follow-up (
      • Mueller A.
      • Kiesewetter F.
      • Binder H.
      • Beckmann M.W.
      • Dittrich R.
      Long-Term Administration of Testosterone Undecanoate Every 3 Months for Testosterone Supplementation in Female-to-Male Transsexuals.
      ). One retrospective case series by
      • Grimstad F.W.
      • Fowler K.G.
      • New E.P.
      • Ferrando C.A.
      • Pollard R.R.
      • Chapman G.
      • Gomez-Lobo V.
      • Gray M.
      Uterine pathology in transmasculine persons on testosterone: a retrospective multicenter case series.
      described 23 documented TVUs of transmasculine people before GAS. In this study, the mean endometrial thickness was 4.9 mm (SD 2.1) (95% CI of 4.0 to 5.9).
      In the present cohort, 47% of transmasculine people previously used GnRHa during their medical transition and 29% were still using it at time of TVU. On the basis of their ability to bind to GnRH receptors and to interfere with the activity of natural GnRH, GnRHa are key regulators in the reproductive hormone cascade. Gonadotrophin releasing hormone agonist affects the endometrium by inducing a hypogonadal state by blockading ovarian oestrogen secretion, resulting in amenorrhoea. Secondary, locally expressed GnRH receptors are also associated with a significant antiproliferative activity of the endometrium (
      • Maggi R.
      • Cariboni A.M.
      • Marelli M.M.
      • Moretti R.M.
      • Andrè V.
      • Marzagalli M.
      • Limonta P.
      GnRH and GnRH receptors in the pathophysiology of the human female reproductive system.
      ). Consequently, current GnRHa use was the most important anticipated, and only confirmed, confounder in the study. Nevertheless, after correcting for current GnRHa use, the difference in endometrial thickness between transmasculine people and cisgender controls remained statistically significant. As the desensitizing effect of GnRHa is completely reversible after prolonged discontinuation, prior GnRHa use was not anticipated to be a possible confounder (
      • Maggi R.
      • Cariboni A.M.
      • Marelli M.M.
      • Moretti R.M.
      • Andrè V.
      • Marzagalli M.
      • Limonta P.
      GnRH and GnRH receptors in the pathophysiology of the human female reproductive system.
      ).
      A known risk factor for developing endometrial cancer is oestradiol unopposed by progesterone (
      • Amant F.
      • Moerman P.
      • Neven P.
      • Timmerman D.
      • Van Limbergen E.
      • Vergote I.
      Endometrial cancer.
      ;
      • Barry J.A.
      • Azizia M.M.
      • Hardiman P.J.
      Risk of endometrial, ovarian and breast cancer in women with polycystic ovary syndrome: a systematic review and meta-analysis.
      ;
      • Grimstad F.W.
      • Fowler K.G.
      • New E.P.
      • Ferrando C.A.
      • Pollard R.R.
      • Chapman G.
      • Gomez-Lobo V.
      • Gray M.
      Uterine pathology in transmasculine persons on testosterone: a retrospective multicenter case series.
      ), possibly still present in transmasculine people undergoing GAHT. Other risk factors for developing endometrial cancer are obesity and increasing age, with the highest incidence around 70 years of age in postmenopausal cisgender women (
      • Amant F.
      • Moerman P.
      • Neven P.
      • Timmerman D.
      • Van Limbergen E.
      • Vergote I.
      Endometrial cancer.
      ). In the present cohort, the duration of testosterone use was short (mean 30.2 months), and the participants were young (median age in transmasculine people 22.6 years and 34.0 years in controls), making it overall unlikely to find a pathologic thick endometrium. In clinical practice, the mean age of the transmasculine population is still relatively young. This makes long-term follow-up mandatory as it is important to increase data on pre-menopausal endometrium characteristics. This will facilitate the development of a suitable screening strategy for transmasculine people undergoing GAHT wishing to retain their reproductive organs.
      In the present study, TVU was carried out before GAS under general anaesthesia. This method was deliberately chosen as internal examination, i.e. TVU is burdensome for transmasculine people (
      • van Trotsenburg M.A.A.
      Gynecological Aspects of Transgender Healthcare.
      ;

      Deutsch, M.B., e. (June 2016). UCSF Transgender Care, Department of Family and Community Medicine, University of California San Francisco. Guidelines for the Primary and Gender-Affirming Care of Transgender and Gender Nonbinary People; 2nd edition. transcare.ucsf.edu/guidelines

      ). This reiterates the need for evidence-based recommendations on the need for endometrial screening as the transmasculine patient may be spared a burdensome examination if screening is deemed unnecessary. Although TVU is superior to a transabdominal ultrasound when accurately assessing the endometrium (
      • Coleman B.G.
      • Arger P.H.
      • Grumbach K.
      • Menard M.K.
      • Mintz M.C.
      • Allen K.S.
      • Arenson R.L.
      • Lamon K.A.
      Transvaginal and transabdominal sonography: prospective comparison.
      ), this procedure may be considered a more ethical first step if screening for endometrial pathology is necessary. Transvaginal ultrasound must only be carried out after careful consideration and consultation with the patient.
      At the time of study, the preoperative protocol was to discontinue GAHT for 2–6 weeks before GAS to prevent an additional risk of thrombosis during and after surgery. One potential event as result of GAHT cessation is the possibility of the menstrual cycle reoccurring and consequently the endometrium developing. This preoperative cessation protocol was terminated in 2017 in our clinic, after sufficient reassuring evidence on the risk of thrombosis was published (
      • Defreyne J.
      • Vantomme B.
      • Van Caenegem E.
      • Wierckx K.
      • De Blok C.J.M.
      • Klaver M.
      • Nota N.M.
      • Van Dijk D.
      • Wiepjes C.M.
      • Den Heijer M.
      • T'Sjoen G.
      Prospective evaluation of hematocrit in gender-affirming hormone treatment: results from European Network for the Investigation of Gender Incongruence.
      ). Unfortunately, no data are available on the menstrual cycles of transmasculine people in those weeks of GAHT cessation and on which cycle day their GAS and TVU were carried out.
      In conclusion, endometrial thickness in transmasculine people exposed to exogenous testosterone is significantly lower compared with cisgender women when assessed by TVU. These results reassure us about the postulated increased risk for developing endometrial hyperplasia or cancer in transmasculine people using testosterone. Burdensome routine ultrasound screening in asymptomatic transmasculine people may, therefore, be unnecessary. Further research, however, is necessary to determine the risk of long-term exposure to exogenous testosterone.

      Acknowledgements

      The authors especially want to thank the DCOG LATER-VEVO study group (Dutch Childhood Oncology Group - Long term Effects after Childhood Cancer/Fertility, Ovarian Reserve and Premature Menopause (Dutch acronym) in the Netherlands for our collaboration.

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      Biography

      Joyce Asseler is a PhD student at the Amsterdam UMC researching the safety of testosterone and fertility in gender diverse persons. Furthermore, she is MD at the Centre of Expertise on Gender Dysphoria at the Amsterdam UMC providing gynaecological care and fertility counselling for gender diverse persons.
      Key message
      Transmasculine people with at least 1 year of gender affirming hormone therapy (testosterone), have a significantly thinner endometrium, as assessed by transvaginal ultrasound, compared with cisgender women. These results suggest an absence of endometrial proliferation by exogenous testosterone. Burdensome endometrial screening in asymptomatic transmasculine persons may, therefore, be unnecessary.