AbstractSTUDY QUESTIONWhat is the impact of co-designed, evidence-based information regarding the anti-Mullerian hormone (AMH) test on women’s interest in having the test?SUMMARY ANSWERWomen who viewed the evidence-based information about the AMH test had lower interest in having an AMH test than women who viewed information produced by an online company selling the test direct-to-consumers.WHAT IS KNOWN ALREADYOnline information about AMH testing often has unfounded claims about its ability to predict fertility and conception, and evidence suggests that women seek out and are recommended the AMH test as a measure of their fertility potential.STUDY DESIGN, SIZE, DURATIONAn online randomized trial was conducted from November to December 2022. Women were randomized (double-blind, equal allocation) to view one of two types of information: co-designed, evidence-based information about the AMH test (intervention), or existing information about the AMH test from a website which markets the test direct-to-consumers (control). A total of 967 women were included in the final analysis.PARTICIPANTS/MATERIALS, SETTING, METHODSParticipants were women recruited through an online panel, who were aged 25–40 years, living in Australia or The Netherlands, had never given birth, were not currently pregnant but would like to have a child now or in the future, and had never had an AMH test. The primary outcome was interest in having an AMH test (seven-point scale; 1 = definitely NOT interested to 7 = definitely interested). Secondary outcomes included attitudes, knowledge, and psychosocial and behavioural outcomes relating to AMH testing.MAIN RESULTS AND THE ROLE OF CHANCEWomen who viewed the evidence-based information about the AMH test had lower interest in having an AMH test (MD = 1.05, 95% CI = 0.83–1.30), less positive attitudes towards (MD = 1.29, 95% CI = 4.57–5.70), and higher knowledge about the test than women who viewed the control information (MD = 0.75, 95% CI = 0.71–0.82).LIMITATIONS, REASONS FOR CAUTIONThe sample was more highly educated than the broader Australian and Dutch populations and some measures (e.g. influence on family planning) were hypothetical in nature.WIDER IMPLICATIONS OF THE FINDINGSWomen have higher knowledge of and lower interest in having the AMH test when given evidence-based information about the test and its limitations. Despite previous studies suggesting women are enthusiastic about AMH testing to learn about their fertility potential, we demonstrate that this enthusiasm does not hold when they are informed about the test’s limitations.STUDY FUNDING/COMPETING INTEREST(S)This project was supported by an NHMRC Emerging Leader Research Fellowship (2009419) and the Australian Health Research Alliance’s Women’s Health Research, Translation and Impact Network EMCR award. B.W.M. reports consultancy for ObsEva and Merck and travel support from Merck. D.L. is the Medical Director of, and holds stock in, City Fertility NSW and reports consultancy for Organon and honoraria from Ferring, Besins, and Merck. K.H. reports consultancy and travel support from Merck and Organon. K.M. is a director of Health Literacy Solutions that owns a licence of the Sydney Health Literacy Lab Health Literacy Editor. No other relevant disclosures exist.TRIAL REGISTRATION NUMBERACTRN12622001136796.TRIAL REGISTRATION DATE17 August 2022.DATE OF FIRST PATIENT’S ENROLMENT21 November 2022.