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Objectives: To develop a checklist to screen, for trustworthiness, papers reporting the results of randomised controlled trials (RCTs). Design: A screening tool was developed using the four-stage approach proposed by Moher et al. This included defining the scope, reviewing the evidence base, suggesting a list of items from piloting, and holding a consensus meeting as part of a Delphi method. The initial checklist was set-up by a core group who had been involved in the assessment of dubious RCTs for several years. We piloted this in a Delphi panel of several stakeholders, including health professionals, reviewers, journal editors, policymakers, researchers and evidence-synthesis specialists. Each member was asked to score three articles with the checklist and the the results were then discussed in two Delphi sessions. Results: The Trustworthiness in RAndomised Clinical Trials (TRACT) checklist includes seven domains that are applicable to every RCT: governance, author group, plausibility of intervention usage, timeframe, drop-out rates, baseline characteristics and outcomes. Each domain contains two or three signalling questions that can be answered as either no concerns, some concerns/no information, or major concerns. If a study is assessed and found to have significant concerns, then editors or reviewers should consider a more thorough investigation, including assessment of original individual participant data. Conclusions: The TRACT checklist is the first checklist developed in a formal process to detect trustworthiness issues in RCTs. It might help editors, publishers and researchers to screen for such issues in submitted or published RCTs in a transparent and replicable manner.

Objective To give an overview of the available methods to investigate research misconduct in health-related research. Study Design and Setting In this scoping review, we conducted a literature search in MEDLINE, Embase, The Cochrane CENTRAL Register of Studies Online (CRSO), and The Virtual Health Library portal up to July 2020. We included papers that mentioned and/or described methods for screening or assessing research misconduct in health-related research. We categorized identified methods into the following four groups according to their scopes: overall concern, textual concern, image concern, and data concern. Results We included 57 papers reporting on 27 methods: two on overall concern, four on textual concern, three on image concern, and 18 on data concern. Apart from the methods to locate textual plagiarism and image manipulation, all other methods, be it theoretical or empirical, are based on examples, are not standardized, and lack formal validation. Conclusion Existing methods cover a wide range of issues regarding research misconduct. Although measures to counteract textual plagiarism are well implemented, tools to investigate other forms of research misconduct are rudimentary and labour-intensive. To cope with the rising challenge of research misconduct, further development of automatic tools and routine validation of these methods is needed. Trial registration number Center for Open Science (OSF) ( https://osf.io/mq89w ).

Background In 2019, a randomized controlled trial (RCT) authored by Dr. Ismail was retracted due to concerns about data integrity. Since there are no policies in place to investigate other publications of authors of retracted studies, we investigated Dr. Ismail’s other trials. Methods We searched for RCTs authored by Dr. Ismail. We made pairwise comparisons of values in baseline and outcome tables between trials. We assessed whether the distributions of baseline characteristics were compatible with properly conducted randomization, using Monte Carlo simulations and the Kolmogorov-Smirnov test. We read the publications carefully for unusual features. Results Dr. Ismail was author in eight published and one unpublished trial. In three of his first author studies we found multiple identical values in the baseline and/or outcome tables from different trials. At least some of the trials were unlikely to have followed a proper randomization process. There were a number of other unusual features in the papers we reviewed. Conclusions It is probable that other trials published by Dr. Ismail contain questionable data. We call for a thorough investigation of the original trial data and related official documents. Our exercise suggests that the practice to assess research integrity should include all publications of authors with retracted fabricated articles.

STUDY QUESTION Is endometrial thickness (EMT) a biomarker to select between women who should switch to gonadotropins and those who could continue clomiphene citrate (CC) after six failed ovulatory cycles? SUMMARY ANSWER Using a cut-off of 7 mm for EMT, we can distinguish between women who are better off switching to gonadotropins and those who could continue CC after six earlier failed ovulatory CC cycles. WHAT IS ALREADY KNOWN For women with normogonadotropic anovulation, CC has been a long-standing first-line treatment in conjunction with intercourse or intrauterine insemination (IUI). We recently showed that a switch to gonadotropins increases the chance of live birth by 11% in these women over continued treatment with CC after six failed ovulatory cycles, at a cost of €15 258 per additional live birth. It is unclear whether EMT can be used to identify women who can continue on CC with similar live birth rates without the extra costs of gonadotropins. STUDY DESIGN, SIZE, DURATION Between 8 December 2008 and 16 December 2015, 666 women with CC failure were randomly assigned to receive an additional six cycles with a change to gonadotropins (n = 331) or an additional six cycles continuing with CC (n = 335), both in conjunction with intercourse or IUI. The primary outcome was conception leading to live birth within 8 months after randomisation. EMT was measured mid-cycle before randomisation during their sixth ovulatory CC cycle. The EMT was available in 380 women, of whom 190 were allocated to gonadotropins and 190 were allocated to CC. PARTICIPANTS/MATERIALS, SETTING, METHODS EMT was determined in the sixth CC cycle prior to randomisation. We tested for interaction of EMT with the treatment effect using logistic regression. We performed a spline analysis to evaluate the association of EMT with chance to pregnancy leading to a live birth in the next cycles and to determine the best cut-off point. On the basis of the resulting cut-off point, we calculated the relative risk and 95% CI of live birth for gonadotropins versus CC at EMT values below and above this cut-off point. Finally, we calculated incremental cost-effectiveness ratios (ICER). MAIN RESULTS AND THE ROLE OF CHANCE Mid-cycle EMT in the sixth cycle interacted with treatment effect (P 7 mm. Among the women with EMT ≤ 7 mm, gonadotropins resulted in a live birth in 44 of 79 women (56%), while CC resulted in a live birth in 28 of 83 women (34%) (RR 1.57, 95% CI 1.13–2.19). Per additional live birth with gonadotropins, the ICER was €9709 (95% CI: €5117 to €25 302). Among the women with EMT > 7 mm, gonadotropins resulted in a live birth in 53 of 111 women (48%) while CC resulted in a live birth in 52 of 107 women (49%) (RR 0.98, 95% CI 0.75–1.29). LIMITATIONS, REASONS FOR CAUTION This was a post hoc analysis of a randomised controlled trial (RCT) and therefore mid-cycle EMT measurements before randomisation during their sixth ovulatory CC cycle were not available for all included women. WIDER IMPLICATIONS OF THE FINDINGS In women with six failed ovulatory cycles on CC and an EMT ≤ 7 mm in the sixth cycle, we advise switching to gonadotropins, since it improves live birth rate over continuing treatment with CC at an extra cost of €9709 to achieve one additional live birth. If the EMT > 7 mm, we advise to continue treatment with CC, since live birth rates are similar to those with gonadotropins, without the extra costs. STUDY FUNDING/COMPETING INTEREST(S) The original MOVIN trial received funding from the Dutch Organization for Health Research and Development (ZonMw number: 80-82310-97-12067). C.B.L.A. reports unrestricted grant support from Merck and Ferring. B.W.M. is supported by a NHMRC Practitioner Fellowship (GNT1082548) and reports consultancy for Merck, ObsEva, IGENOMIX and Guerbet. All other authors have nothing to declare. TRIAL REGISTRATION NUMBER Netherlands Trial Register, number NTR1449

While updating a systematic review on the topic of ovulation of induction, we observed unusual similarities in a number of randomised controlled trials (RCTs) published by two authors from the same institute in the same disease spectrum in a short period of time. We therefore undertook a focused analysis of the data integrity of all RCTs published by the two authors. We made pairwise comparisons to find identical or similar values in baseline characteristics and outcome tables between trials. We also assessed whether baseline characteristics were compatible with chance, using Monte Carlo simulations and Kolmogorov-Smirnov test. For 35 trials published between September 2006 and January 2016, we found a large number of similarities in both the baseline characteristics and outcomes of 26. Analysis of the baseline characteristics of the trials indicated that their distribution was unlikely to be the result of proper randomisation. The procedures demonstrated in this paper may help to assess data integrity in future attempts to verify the authenticity of published RCTs.

BACKGROUND In our recent individual participant data (IPD) meta-analysis evaluating the effectiveness of first-line ovulation induction for polycystic ovary syndrome (PCOS), IPD were only available from 20 studies of 53 randomized controlled trials (RCTs). We noticed that the summary effect sizes of meta-analyses of RCTs without IPD sharing were different from those of RCTs with IPD sharing. Granting access to IPD for secondary analysis has implications for promoting fair and transparent conduct of RCTs. It is, however, still common for authors to choose to withhold IPD, limiting the impact of and confidence in the results of RCTs and systematic reviews based on aggregate data. OBJECTIVE AND RATIONALE We performed a meta-epidemiologic study to elucidate if RCTs without IPD sharing have lower quality and more methodological issues than those with IPD sharing in an IPD meta-analysis evaluating first-line ovulation induction for PCOS. SEARCH METHODS We included RCTs identified for the IPD meta-analysis. We dichotomized RCTs according to whether they provided IPD (shared group) or not (non-shared group) in the IPD meta-analysis. We restricted RCTs to full-text published trials written in English. We assessed and compared RCTs in the shared and non-shared groups on the following criteria: Risk of Bias (RoB 2.0), GRADE approach, adequacy of trial registration; description of statistical methods and reproducibility of univariable statistical analysis; excessive similarity or difference in baseline characteristics that is not compatible with chance; and other miscellaneous methodological issues. OUTCOMES In total, 45 trials (8697 women) were included in this study. IPD were available from 17 RCTs and 28 trials were categorized as the non-shared IPD group. Pooled risk rates obtained from the shared and non-shared groups were different. Overall low risk of bias was associated with 13/17 (76%) of shared RCTs versus 7/28 (25%) of non-shared RCTs. For RCTs that started recruitment after 1 July 2005, adequate trial registration was found in 3/9 (33%) of shared IPD RCTs versus 0/16 (0%) in non-shared RCTs. In total, 7/17 (41%) of shared RCTs and 19/28 (68%) of non-shared RCTs had issues with the statistical methods described. The median (range) of inconsistency rate per study, between reported and reproduced analyses for baseline variables, was 0% (0–92%) (6 RCTs applicable) in the shared group and 54% (0–100%) (13 RCTs applicable) in the non-shared group. The median (range) of inconsistency rate of univariable statistical results for the outcome(s) per study was 0% (0–63%) (14 RCTs applicable) in the shared group and 44% (0–100%) (24 RCTs applicable) in the non-shared group. The distributions of simulation-generated P-values from comparisons of baseline continuous variables between intervention and control arms suggested that RCTs in the shared group are likely to be consistent with properly conducted randomization (P = 0.163), whereas this was not the case for the RCTs in the non-shared group (P = 4.535 × 10−8). WIDER IMPLICATIONS IPD meta-analysis on evaluating first-line ovulation induction for PCOS preserves validity and generates more accurate estimates of risk than meta-analyses using aggregate data, which enables more transparent assessments of benefits and risks. The availability of IPD and the willingness to share these data may be a good indicator of quality, methodological soundness and integrity of RCTs when they are being considered for inclusion in systematic reviews and meta-analyses.

BACKGROUND: Polycystic ovary syndrome (PCOS) is a common condition affecting 8% to 13% of reproductive‐aged women. In the past clomiphene citrate (CC) used to be the first‐line treatment in women with PCOS. Ovulation induction with letrozole should be the first‐line treatment according to new guidelines, but the use of letrozole is off‐label. Consequently, CC is still commonly used. Approximately 20% of women on CC do not ovulate. Women who are CC‐resistant can be treated with gonadotrophins or other medical ovulation‐induction agents. These medications are not always successful, can be time‐consuming and can cause adverse events like multiple pregnancies and cycle cancellation due to an excessive response. Laparoscopic ovarian drilling (LOD) is a surgical alternative to medical treatment. There are risks associated with surgery, such as complications from anaesthesia, infection, and adhesions. OBJECTIVES: To evaluate the effectiveness and safety of LOD with or without medical ovulation induction compared with medical ovulation induction alone for women with anovulatory polycystic PCOS and CC‐resistance. SEARCH METHODS: We searched the Cochrane Gynaecology and Fertility Group (CGFG) trials register, CENTRAL, MEDLINE, Embase, PsycINFO, CINAHL and two trials registers up to 8 October 2019, together with reference checking and contact with study authors and experts in the field to identify additional studies. SELECTION CRITERIA: We included randomised controlled trials (RCTs) of women with anovulatory PCOS and CC resistance who underwent LOD with or without medical ovulation induction versus medical ovulation induction alone, LOD with assisted reproductive technologies (ART) versus ART, LOD with second‐look laparoscopy versus expectant management, or different techniques of LOD. DATA COLLECTION AND ANALYSIS: Two review authors independently selected studies, assessed risks of bias, extracted data and evaluated the quality of the evidence using the GRADE method. The primary effectiveness outcome was live birth and the primary safety outcome was multiple pregnancy. Pregnancy, miscarriage, ovarian hyperstimulation syndrome (OHSS), ovulation, costs, and quality of life were secondary outcomes. MAIN RESULTS: This updated review includes 38 trials (3326 women). The evidence was very low‐ to moderate‐quality; the main limitations were due to poor reporting of study methods, with downgrading for risks of bias (randomisation and allocation concealment) and lack of blinding. Laparoscopic ovarian drilling with or without medical ovulation induction versus medical ovulation induction alone Pooled results suggest LOD may decrease live birth slightly when compared with medical ovulation induction alone (odds ratio (OR) 0.71, 95% confidence interval (CI) 0.54 to 0.92; 9 studies, 1015 women; I(2) = 0%; low‐quality evidence). The evidence suggest that if the chance of live birth following medical ovulation induction alone is 42%, the chance following LOD would be between 28% and 40%. The sensitivity analysis restricted to only RCTs with low risk of selection bias suggested there is uncertainty whether there is a difference between the treatments (OR 0.90, 95% CI 0.59 to 1.36; 4 studies, 415 women; I(2) = 0%, low‐quality evidence). LOD probably reduces multiple pregnancy rates (Peto OR 0.34, 95% CI 0.18 to 0.66; 14 studies, 1161 women; I(2) = 2%; moderate‐quality evidence). This suggests that if we assume the risk of multiple pregnancy following medical ovulation induction is 5.0%, the risk following LOD would be between 0.9% and 3.4%. Restricting to RCTs that followed women for six months after LOD and six cycles of ovulation induction only, the results for live birth were consistent with the main analysis. There may be little or no difference between the treatments for the likelihood of a clinical pregnancy (OR 0.86, 95% CI 0.72 to 1.03; 21 studies, 2016 women; I(2) = 19%; low‐quality evidence). There is uncertainty about the effect of LOD compared with ovulation induction alone on miscarriage (OR 1.11, 95% CI 0.78 to 1.59; 19 studies, 1909 women; I(2) = 0%; low‐quality evidence). OHSS was a very rare event. LOD may reduce OHSS (Peto OR 0.25, 95% CI 0.07 to 0.91; 8 studies, 722 women; I(2) = 0%; low‐quality evidence). Unilateral LOD versus bilateral LOD Due to the small sample size, the quality of evidence is insufficient to justify a conclusion on live birth (OR 0.83, 95% CI 0.24 to 2.78; 1 study, 44 women; very low‐quality evidence). There were no data available on multiple pregnancy. The likelihood of a clinical pregnancy is uncertain between the treatments, due to the quality of the evidence and the large heterogeneity between the studies (OR 0.57, 95% CI 0.39 to 0.84; 7 studies, 470 women; I(2) = 60%, very low‐quality evidence). Due to the small sample size, the quality of evidence is not sufficient to justify a conclusion on miscarriage (OR 1.02, 95% CI 0.31 to 3.33; 2 studies, 131 women; I(2) = 0%; very low‐quality evidence). Other comparisons Due to lack of evidence and very low‐quality data there is uncertainty whether there is a difference for any of the following comparisons: LOD with IVF versus IVF, LOD with second‐look laparoscopy versus expectant management, monopolar versus bipolar LOD, and adjusted thermal dose versus fixed thermal dose. AUTHORS' CONCLUSIONS: Laparoscopic ovarian drilling with and without medical ovulation induction may decrease the live birth rate in women with anovulatory PCOS and CC resistance compared with medical ovulation induction alone. But the sensitivity analysis restricted to only RCTs at low risk of selection bias suggests there is uncertainty whether there is a difference between the treatments, due to uncertainty around the estimate. Moderate‐quality evidence shows that LOD probably reduces the number of multiple pregnancy. Low‐quality evidence suggests that there may be little or no difference between the treatments for the likelihood of a clinical pregnancy, and there is uncertainty about the effect of LOD compared with ovulation induction alone on miscarriage. LOD may result in less OHSS. The quality of evidence is insufficient to justify a conclusion on live birth, clinical pregnancy or miscarriage rate for the analysis of unilateral LOD versus bilateral LOD. There were no data available on multiple pregnancy.

BACKGROUND Polycystic ovary syndrome (PCOS) is the most frequent cause of anovulatory infertility. In women with PCOS, effective ovulation induction serves as an important first-line treatment for anovulatory infertility. Individual participant data (IPD) meta-analysis is considered as the gold standard for evidence synthesis which provides accurate assessments of outcomes from primary randomised controlled trials (RCTs) and allows additional analyses for time-to-event outcomes. It also facilitates treatment–covariate interaction analyses and therefore offers an opportunity for personalised medicine. OBJECTIVE AND RATIONALE We aimed to evaluate the effectiveness of different ovulation induction agents, in particular letrozole alone and clomiphene citrate (CC) plus metformin, as compared to CC alone, as the first-line choice for ovulation induction in women with PCOS and infertility, and to explore interactions between treatment and participant-level baseline characteristics. SEARCH METHODS We searched electronic databases including MEDLINE, EMBASE and Cochrane Central Register of Controlled Trials up to 20 December 2018. We included RCTs comparing the following interventions with each other or placebo/no treatment in women with PCOS and infertility: CC, metformin, CC plus metformin, letrozole, gonadotrophin and tamoxifen. We excluded studies on treatment-resistant women. The primary outcome was live birth. We contacted the investigators of eligible RCTs to share the IPD and performed IPD meta-analyses. We assessed the risk of bias by using the Cochrane risk of bias tool for RCTs. OUTCOMES IPD of 20 RCTs including 3962 women with PCOS were obtained. Six RCTs compared letrozole and CC in 1284 women. Compared with CC, letrozole improved live birth rates (3 RCTs, 1043 women, risk ratio [RR] 1.43, 95% confidence interval [CI] 1.17–1.75, moderate-certainty evidence) and clinical pregnancy rates (6 RCTs, 1284 women, RR 1.45, 95% CI 1.23–1.70, moderate-certainty evidence) and reduced time-to-pregnancy (6 RCTs, 1235 women, hazard ratio [HR] 1.72, 95% CI 1.38–2.15, moderate-certainty evidence). Meta-analyses of effect modifications showed a positive interaction between baseline serum total testosterone levels and treatment effects on live birth (interaction RR 1.29, 95% CI 1.01–1.65). Eight RCTs compared CC plus metformin to CC alone in 1039 women. Compared with CC alone, CC plus metformin might improve clinical pregnancy rates (8 RCTs, 1039 women, RR 1.18, 95% CI 1.00–1.39, low-certainty evidence) and might reduce time-to-pregnancy (7 RCTs, 898 women, HR 1.25, 95% CI 1.00–1.57, low-certainty evidence), but there was insufficient evidence of a difference on live birth rates (5 RCTs, 907 women, RR 1.08, 95% CI 0.87–1.35, low-certainty evidence). Meta-analyses of effect modifications showed a positive interaction between baseline insulin levels and treatment effects on live birth in the comparison between CC plus metformin and CC (interaction RR 1.03, 95% CI 1.01–1.06). WIDER IMPLICATIONS In women with PCOS, letrozole improves live birth and clinical pregnancy rates and reduces time-to-pregnancy compared to CC and therefore can be recommended as the preferred first-line treatment for women with PCOS and infertility. CC plus metformin may increase clinical pregnancy and may reduce time-to-pregnancy compared to CC alone, while there is insufficient evidence of a difference on live birth. Treatment effects of letrozole are influenced by baseline serum levels of total testosterone, while those of CC plus metformin are affected by baseline serum levels of insulin. These interactions between treatments and biomarkers on hyperandrogenaemia and insulin resistance provide further insights into a personalised approach for the management of anovulatory infertility related to PCOS.

Study question In women undergoing IVF or ICSI cycles, do recombinant gonadotrophins differ from urinary-derived highly purified human menopausal gonadotropin (HP-hMG) or highly purified follicle-stimulating hormone (HP-FSH) in the total amount of gonadotrophins required to reach a live birth? Summary answer The difference between recombinant and urinary-derived HP-hMG or HP-FSH in the required amount to reach a live birth in IVF/ICSI cycles appears small. What is known already At present, gynecologists can choose between recombinant FSH (rFSH), urinary-derived HP-hMG and HP-FSH. These products are equally effective and safe, but it is unknown how these gonadotrophins compare in terms of IU required to reach a live birth. Study design size and duration We conducted a search in Medline, Embase and CINAHL up to July 2018. We included randomized controlled trials (RCTs) that compared rFSH with HP-hMG or HP-FSH for ovarian stimulation in couples scheduled for IVF or ICSI treatment. From each randomized trial, we extracted the outcome data and information on participants, methods, interventions and funding. Participants/materials setting and methods Women undergoing ovarian stimulation with rFSH, HP-hMG or HP-FSH were included. We extracted data for the mean amount of gonadotrophins with SD, clinical pregnancy rate, live birth rate and cumulative live birth rate per woman from the included RCTs. We summarized these outcomes by calculating the individual and pooled mean difference (MD) or relative risk (RR) with 95% CI. We used the Review Manager software to perform the meta-analyses. We applied a random effect model to pool the data. We estimated the total amount of gonadotrophins used per extra live birth by STATA 14.2 and R software. Main results and the role of chance A total of 28 studies with 7553 women were included in this review, of which 24 studies provided information on the total amount of gonadotrophins per woman who started an IVF/ICSI cycle. The total amount of gonadotrophins varied significantly between studies. The MDs in total amount were -37 IU (seven studies; N = 3220; 95% CI, -115 to 41; I 2 = 68%) for rFSH versus HP-hMG and -31 IU (17 studies; N = 3629; 95% CI, -290 to 228; I 2 = 97%) for rFSH versus HP-FSH. For rFSH versus HP-hMG, the RR for clinical pregnancy, live birth and cumulative live birth were 0.90 (95% CI, 0.81-1.00), 0.88 (95% CI, 0.78-0.99) and 0.91 (95% CI, 0.80-1.04), respectively. For rFSH versus HP-FSH, the RR for clinical pregnancy and live birth were 1.03 (95% CI, 0.94-1.13) and 1.03 (95% CI, 0.90-1.18), respectively; the data on cumulative live birth rate were lacking. The estimated difference in mean gonadotrophin amount per extra live birth was 789 IU (95% CI, -9.5 to 1570) for rFSH versus HP-hMG and -365 IU (95% CI, -2675 to 1945) for rFSH versus HP-FSH. Limitations reasons for caution There was severe heterogeneity in the total amount of gonadotrophins between studies. A small fraction of women did not start gonadotrophin treatment; this was usually not accounted for in the provided mean amount of gonadotrophins per study and might have affected the averaged total amount of gonadotrophins but is unlikely to have affected the differences in the amount between rFSH and HP-hMG or HP-FSH. Wider implications of the findings The differences in the required amount to reach a live birth between rFSH, HP-hMG and HP-FSH appear to be small. Decision-making should be based on convenience, availability, actual costs and patient preferences. Study funding/competing interests The authors declare no conflict of interest. No external funding was either sought or obtained for this study. Registration number Prospero CRD42016038238.

Background: Clomiphene citrate (CC) is generally considered first-line treatment in women with anovulation due to polycystic ovary syndrome (PCOS). Ovulation induction with follicle-stimulating hormone (FSH; gonadotrophins) is second-line treatment for women who do not ovulate or conceive while taking CC. Metformin may increase the effectiveness of ovulation induction with gonadotrophins and may promote safety by preventing multiple pregnancy. Objectives: To determine the effectiveness and safety of metformin co-treatment during ovulation induction with gonadotrophins with respect to rates of live birth and multiple pregnancy in women with PCOS. Search methods: We searched the Cochrane Gynaecology and Fertility (CGF) Group specialised register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, Embase, PsycINFO and the Cumulative Index to Nursing and Allied Health Literature (CINAH) on 8 June 2016, and the reference lists of included and other relevant studies. We searched ongoing trials registries in the World Health Organization (WHO) portal and on clinicaltrials.gov on 4 September 2016. Selection criteria: We included randomised controlled trials (RCTs) reporting data on comparison of clinical outcomes in women with PCOS undergoing ovulation induction with gonadotrophins plus metformin versus gonadotrophins alone or gonadotrophins plus placebo. Data collection and analysis: We used standard methodological procedures recommended by Cochrane. Primary review outcomes were live birth rate and multiple pregnancy rate. Secondary outcomes were ovulation rate, clinical pregnancy rate, ovarian hyperstimulation syndrome (OHSS) rate, miscarriage rate, cycle cancellation rate and adverse effects. Main results: We included five RCTs (with 264 women) comparing gonadotrophins plus metformin versus gonadotrophins. The gonadotrophin used was recombinant FSH in four studies and highly purified FSH in one study. Evidence was of low quality: The main limitations were serious risk of bias due to poor reporting of study methods and blinding of participants and outcome assessors. Live birth Metformin plus FSH was associated with a higher cumulative live birth rate when compared with FSH (odds ratio (OR) 2.31, 95% confidence interval (CI) 1.23 to 4.34; two RCTs, n = 180; I2 = 0%; low-quality evidence). This suggests that if the chance of live birth after FSH is assumed to be 27%, then the chance after addition of metformin would be between 32% and 60%. Other pregnancy outcomes Metformin use was associated with a higher ongoing pregnancy rate (OR 2.46, 95% CI 1.36 to 4.46; four RCTs, n = 232; I2 = 0%; low-quality evidence) and a higher clinical pregnancy rate (OR 2.51, 95% CI 1.46 to 4.31; five RCTs, n = 264; I2 = 0%; low-quality evidence). Multiple pregnancy Results showed no evidence of a difference in multiple pregnancy rates between metformin plus FSH and FSH (OR 0.55, 95% CI 0.15 to 1.95; four RCTs, n = 232; I2 = 0%; low-quality evidence) and no evidence of a difference in rates of miscarriage or OHSS. Other adverse effects Evidence was inadequate as the result of limited available data on adverse events after metformin compared with after no metformin (OR 1.78, 95% CI 0.39 to 8.09; two RCTs, n = 91; I2 = 0%; very low-quality evidence). Authors' conclusions: Preliminary evidence suggests that metformin may increase the live birth rate among women undergoing ovulation induction with gonadotrophins. At this moment, evidence is insufficient to show an effect of metformin on multiple pregnancy rates and adverse events. Additional trials are necessary before we can provide further conclusions that may affect clinical practice.