Abstract STUDY QUESTION What are the costs and effects of tubal patency testing by hysterosalpingo-foam sonography (HyFoSy) compared to hysterosalpingography (HSG) in infertile women during the fertility work-up? SUMMARY ANSWER During the fertility work-up, clinical management based on the test results of HyFoSy leads to slightly lower, though not statistically significant, live birth rates, at lower costs, compared to management based on HSG results. WHAT IS KNOWN ALREADY Traditionally, tubal patency testing during the fertility work-up is performed by HSG. The FOAM trial, formally a non-inferiority study, showed that management decisions based on the results of HyFoSy resulted in a comparable live birth rate at 12 months compared to HSG (46% versus 47%; difference −1.2%, 95% CI: −3.4% to 1.5%; P = 0.27). Compared to HSG, HyFoSy is associated with significantly less pain, it lacks ionizing radiation and exposure to iodinated contrast medium. Moreover, HyFoSy can be performed by a gynaecologist during a one-stop fertility work-up. To our knowledge, the costs of both strategies have never been compared. STUDY DESIGN, SIZE, DURATION We performed an economic evaluation alongside the FOAM trial, a randomized multicenter study conducted in the Netherlands. Participating infertile women underwent, both HyFoSy and HSG, in a randomized order. The results of both tests were compared and women with discordant test results were randomly allocated to management based on the results of one of the tests. The follow-up period was twelve months. PARTICIPANTS/MATERIALS, SETTING, METHODS We studied 1160 infertile women (18–41 years) scheduled for tubal patency testing. The primary outcome was ongoing pregnancy leading to live birth. The economic evaluation compared costs and effects of management based on either test within 12 months. We calculated incremental cost-effectiveness ratios (ICERs): the difference in total costs and chance of live birth. Data were analyzed using the intention to treat principle. MAIN RESULTS AND THE ROLE OF CHANCE Between May 2015 and January 2019, 1026 of the 1160 women underwent both tubal tests and had data available: 747 women with concordant results (48% live births), 136 with inconclusive results (40% live births), and 143 with discordant results (41% had a live birth after management based on HyFoSy results versus 49% with live birth after management based on HSG results). When comparing the two strategies—management based on HyfoSy results versus HSG results—the estimated chance of live birth was 46% after HyFoSy versus 47% after HSG (difference −1.2%; 95% CI: −3.4% to 1.5%). For the procedures itself, HyFoSy cost €136 and HSG €280. When costs of additional fertility treatments were incorporated, the mean total costs per couple were €3307 for the HyFoSy strategy and €3427 for the HSG strategy (mean difference €−119; 95% CI: €−125 to €−114). So, while HyFoSy led to lower costs per couple, live birth rates were also slightly lower. The ICER was €10 042, meaning that by using HyFoSy instead of HSG we would save €10 042 per each additional live birth lost. LIMITATIONS, REASONS FOR CAUTION When interpreting the results of this study, it needs to be considered that there was a considerable uncertainty around the ICER, and that the direct fertility enhancing effect of both tubal patency tests was not incorporated as women underwent both tubal patency tests in this study. WIDER IMPLICATION OF THE FINDINGS Compared to clinical management based on HSG results, management guided by HyFoSy leads to slightly lower live birth rates (though not statistically significant) at lower costs, less pain, without ionizing radiation and iodinated contrast exposure. Further research on the comparison of the direct fertility-enhancing effect of both tubal patency tests is needed. STUDY FUNDING/COMPETING INTEREST(S) FOAM trial was an investigator-initiated study, funded by ZonMw, a Dutch organization for Health Research and Development (project number 837001504). IQ Medical Ventures provided the ExEm®-FOAM kits free of charge. The funders had no role in study design, collection, analysis, and interpretation of the data. K.D. reports travel-and speakers fees from Guerbet and her department received research grants from Guerbet outside the submitted work. H.R.V. received consulting—and travel fee from Ferring. A.M.v.P. reports received consulting fee from DEKRA and fee for an expert meeting from Ferring, both outside the submitted work. C.H.d.K. received travel fee from Merck. F.J.M.B. received a grant from Merck and speakers fee from Besins Healthcare. F.J.M.B. is a member of the advisory board of Merck and Ferring. J.v.D. reported speakers fee from Ferring. J.S. reports a research agreement with Takeda and consultancy for Sanofi on MR of motility outside the submitted work. M.v.W. received a travel grant from Oxford Press in the role of deputy editor for Human Reproduction and participates in a DSMB as independent methodologist in obstetrics studies in which she has no other role. B.W.M. received an investigator grant from NHMRC GNT1176437. B.W.M. reports consultancy for ObsEva, Merck, Guerbet, iGenomix, and Merck KGaA and travel support from Merck KGaA. V.M. received research grants from Guerbet, Merck, and Ferring and travel and speakers fees from Guerbet. The other authors do not report conflicts of interest. TRIAL REGISTRATION NUMBER International Clinical Trials Registry Platform No. NTR4746.