Ovarian Stimulation Strategies for Intrauterine Insemination in Couples with Unexplained Infertility - A Systematic Review and Individual Participant Data Meta-analysis
Intrauterine insemination with ovarian stimulation (IUI-OS) is a first-line treatment for couples with unexplained infertility. Individual participant data meta-analysis (IPD-MA) is the gold standard for evidence synthesis.
Aim
To compare the effectiveness and safety of ovarian stimulation with gonadotrophin, Letrozole and clomiphene citrate (CC) and to explore treatment-covariate interactions for important baseline characteristics in women undergoing IUI.
Method
We searched electronic databases including PubMed, MEDLINE, EMBASE, Cochrane Database of Systematic Reviews, Cochrane Central Register of Controlled Trials (CENTRAL). We included randomised controlled trials (RCTs) comparing IUI-OS with gonadotropins, Letrozole or CC among couples with unexplained infertility. We excluded dose comparing studies of the same drug. We contacted the authors of eligible RCTs to share the IPD and established the IUI IPD-MA collaboration. The primary effectiveness outcome was live birth and the primary safety outcome was multiple pregnancy. We used a one-stage approach using a random effects model.
Results
Six RCTs (n= 2299) provided IPD. Gonadotropins increased the chance of a live birth compared to both CC (5 RCTs, 1946 women, RR 1.28, 95%CI 1.10 to 1.49, I2 = 25%, moderate-quality evidence) whereas there was insufficient evidence of a difference between Letrozole and CC (1 RCT, 599 women, RR 0.77 95%CI 0.58 to 1.03). Gonadotropins increased the risk of a multiple pregnancy compared to both CC (4 RCTs, 1696 women, RR 2.17, 95%CI 1.33 to 3.55, I2 = 69%, low-quality evidence) whereas there was insufficient evidence of a difference between Letrozole and CC (1 RCT, 599 women, RR 0.71, 95%CI 0.33 to 1.56). No strong evidence on the treatment-covariate interactions (female age, BMI or primary versus secondary infertility) was found.
Conclusion
Gonadotropins increased the chance of a live birth compared to both CC and Letrozole but also increased the chance of a multiple pregnancy. Further RCTs comparing Letrozole and other interventions in couples with unexplained infertility are needed.
Check JH et al., 2022·Gynecol Reprod Health·
Open Access
Many infertility specialists advise women with diminished oocyte reserve (DOR) that their remaining oocytes probably are of poor quality similar to women of advanced reproductive age. There have been studies, especially employing in vitro fertilization-embryo transfer (IVF-ET), showing very poor live delivered pregnancy rates despite the transfer of morphologically normal embryos in women even with mild DOR. However, other data suggests that the low pregnancy rates are related to the use of high dosages of follicle stimulating hormone (FSH) drugs which down-regulate some key FSH dependent enzymes, cytokines, or proteins required for proper embryo implantation. Some studies have shown that techniques that favor FSH receptor up-regulation, rather than down-regulation, can provide the chance of live delivery 80% as well in women ≤ 35 with DOR, 70% for women 36-39, and 50% for women 40-42. Though some infertility specialists will encourage women whose only infertility issue is DOR, who reject the initial suggestion to consider donor oocytes, to proceed immediately with IVF-ET to maximize success, pregnancies are quite possible with natural conception. Thus, it seems imprudent to make couples undergo the financial burden of IVF-ET in the absence of a significant tubal or male factor problem. Not only have live deliveries occurred in women with DOR, using the principle described to achieve a mature dominant follicle followed by proper luteal phase support, with serum FSH levels over 100 mIU/mL, but also serum Anti-Mullerian Hormone (AMH) levels that were undetectable. This even applies to women in overt menopause where FSH up-regulation was achieved by negative feedback to the pituitary using ethinyl estradiol inhibiting FSH release, or down-regulation of hypothalamic-pituitary stimulation of FSH production by using gonadotropin releasing hormone agonists or antagonists.
Sharma S et al., 2018·J Hum Reprod Sci·
Open Access
Gonadotropin stimulation is used as the second line of treatment in patients with thin endometrium following clomiphene citrate (CC) administration, which is associated with higher cost, multiple births, and ovarian hyperstimulation syndrome. Tamoxifen (TMX), a selective estrogen receptor modulator, acts as an agonist on the endometrium. The objective of the present study was to compare the efficacy of low-dose CC, TMX, and gonadotropins in women with thin endometrium (<7 mm) following Clomiphene in intrauterine insemination (IUI) cycles. SETTINGS AND A prospective observational study between December 2011 and June 2013 was carried out in a tertiary infertility center. Women (n = 502) undergoing IUI with endometrium <7 mm after 100 mg CC were included in the study and divided into three treatment groups. Women in Group A (n = 182, cycles = 364) received clomiphene (50 mg/day from day 3 to 7), Group B (n = 179, cycles = 342) received TMX (40 mg/day from day 3 to 7), and Group C (n = 141, cycles = 226) received continuous urine-derived follicle-stimulating hormone 75-150 IU from day 3 onward until human chorionic gonadotropin injection. Endometrial thickness (ET), pregnancy rate, and live birth rate were considered as main outcome measures. Multiple comparisons using one-way ANOVA and Schiff's test were performed. Pregnancy and live birth rate were significantly higher (P < 0.004) in TMX and gonadotropin groups compared to clomiphene. A number of follicles in the TMX group were found to be lower (P < 0.001) compared to other two groups. In polycystic ovary syndrome patients, ovulation induction with TMX resulted in inadequate response in more than half of the cycles. TMX can improve ET and live birth rate in patients with thin endometrium after clomiphene.
Reimão Miller KA et al., 2026·Reproductive biomedicine online
This review explores whether the clomiphene citrate stair-step protocol (SSP) for ovulation induction in patients with polycystic ovary syndrome (PCOS) outperforms the traditional protocol. The following databases were searched: PubMed, Cochrane Library, ClinicalTrials.gov, EMBASE and Google Scholar from inception to 15 June 2025, following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and with PROSPERO registration (CRD420251050294). Of 847 screened records, five randomized controlled trials were included (n = 520: n = 255; traditional protocol: n = 265). Analyses were conducted in Review Manager 5.4 using random-effects models. Risk ratios, mean differences and 95% confidence intervals were calculated. Heterogeneity was assessed with I², risk of bias with RoB2, certainty with GRADE and robustness with leave-one-out sensitivity analysis. The SSP increased ovulation rates compared with the traditional protocol (RR 1.28, 95% CI 1.10 to 1.49; five randomized controlled trials [RCTs], n = 520, I² = 0%). Clinical pregnancy also favoured SSP (RR 1.46, 95% CI 1.04 to 2.05; four RCTs, n = 460; I² = 0%), although this result was largely driven by one study. The SSP shortened treatment duration (mean difference -32.59 days, 95% CI -38.66 to -26.52 days; three RCTs, n = 320, I² = 83%). Endometrial thickness was similar (mean difference 0.32 mm, 95% CI -0.95 to 1.59 mm; four RCTs, n = 460, I² = 91%). SSP improves ovulation rate and shortens treatment without affecting endometrial thickness and may increase clinical pregnancy rates.
Restorative Care and Assisted Reproduction · Outcome Comparisons
Restorative Reproductive Medicine (RRM) aims to restore fertility by diagnosing and treating the underlying causes of infertility. RRM is frequently promoted as an alternative to assisted reproductive technology (ART), despite uncertainty regarding its comparative effectiveness and safety. Where delayed childbearing and infertility are becoming more common, reliance on optimization of natural physiology alone may delay effective treatment and compromise reproductive outcomes. A systematic review of the current evidence comparing RRM to either ART or unassisted conception is, therefore, essential to inform clinical practice, guideline development, and shared decision-making for patients experiencing infertility. To assess the effectiveness and safety of RRM approaches, evaluated as a whole, rather than as individual components, compared with ART and medically unassisted conception in couples experiencing infertility. A systematic literature search of MEDLINE, Embase, CENTRAL and the Journal of Restorative Reproductive Medicine from inception to 28 November 2025. We included randomized control trials (RCTs) or nonrandomized comparative studies evaluating reproductive and safety outcomes of RRM as a unified treatment, compared with either ART or expectant management (attempted medically unassisted conception). Two reviewers independently screened titles, abstracts and full texts with disagreements resolved by a third reviewer. We retrieved 724 records, of which 16 studies underwent full-text review. No RCTs or comparative observational studies were identified. All 16 full-text studies were excluded for an ineligible study design (no control group); most were cohort studies in which all participants underwent RRM. Ten studies reported reproductive outcomes; nine of these made claims regarding the benefits or effectiveness of RRM. None of these claims were supported by the study designs used, as the lack of a comparison group precludes reliable estimation of treatment effects. Consequently, these studies cannot provide valid estimates of RRM success rates, nor permit any meaningful inference about its effectiveness relative to unassisted conception or ART. Large-scale RCTs or prospective cohort studies reporting effectiveness and safety outcomes are required to inform evidence-based fertility guidelines. There are no comparative studies to support reliable estimates of the safety and effectiveness of RRM compared with ART or medically unassisted conception for couples experiencing infertility.