Abstract Study question Does dual trigger with co-administration of GnRH agonist and Human Chorionic Gonadotropin (hCG) increase the outcome of Intrauterine Insemination (IUI) compared to hCG alone? Summary answer using the dual trigger for final oocyte maturation increases the clinical pregnancy rate compared to triggering with hCG alone in IUI cycle. What is known already Various techniques are performed to increase the success rates of Intrauterine Insemination (IUI) including sperm preparation, ovarian stimulation, ovulation trigger, and endometrial preparation. The dual trigger of final oocyte maturation with a GnRH-agonist and a standard dosage of hCG increase the outcome of in vitro fertilization (IVF) cycles significantly but this dual trigger has not been used in IUI. Study design, size, duration A single center, retrospective observational study between January 2016 and October 2018 was performed in 639 IUI cycles in Halim Fertility Center (HFC), Division of Reproductive Endocrinology and Infertility, Faculty of Medicine, Universitas Sumatera Utara, Indonesia. Participants/materials, setting, methods Six hundred and thirty-nine IUI cycles were divided into two groups: group I received recombinant hCG alone as the single trigger and group II received GnRH agonist plus recombinant hCG as dual-trigger. Data on patients age,FSH, AMH, total amount of rFSH, sperm quality, endometrial thickness, number of basal antral follicles, number of follicles > 17 mm, clinical pregnancy rate, multiple pregnancy rate and Ovarian hyperstimulation syndrome (OHSS) were assessed and compared between the two groups. Main results and the role of chance Our study included 639 IUI cycles with a dual trigger group (334 IUI cycles) and a single trigger (305 IUI cycles). The age of participants (32 years versus 32 years, P = 0.945), FSH (6.3 mIU/mL versus 6.5 mIU/mL, P = 0.411), AMH (2.7 ng/mL versus 2.4 ng/mL), P = 0.340), total amount of rFSH (900 IU versus 900 IU, P = 0.873), sperm concentration (17.2x106/mL versus 17.3x106/mL, P = 0.488), sperm motility (35% versus 35%, P = 0.847), sperm morphology (5%normal versus 5%normal, P = 0.916), TMSC (13.9x106/ejaculate versus 12.6x106/ejaculate, P = 0.545) were comparable between the two groups. The endometrial thickness (9 mm versus 9 mm, P = 0.337), the number of basal antral follicles (7 versus 7, P = 0.587) and the number of follicles >17mm (2 versus 2, P = 0.974) were also comparable between the two groups. The clinical pregnancy rate (14.1% versus 28.7%, P < 0.001) with RR value 2.524 (95%CI RR 1.681-3.790) was significantly higher in the dual trigger compared to the single trigger group. The multiple pregnancy rate (7% versus 7.3%), P = 0.627) and OHSS rate (2.6% versus 2.7%, P = 0.576) were no significantly difference between the two groups. Limitations, reasons for caution This study is a retrospective study so that data sampling was not well controlled. Data recruitment is based on a period because we modified the ovulation trigger from a single trigger to dual trigger after almost one year then we evaluated the outcome of IUI between the two groups. Wider implications of the findings This is the first study to evaluate the outcome of the dual trigger on ovulation trigger in intrauterine insemination (IUI) in Indonesia. The present study indicates a potential dual trigger might lead to better IUI outcomes and it can be used more widely. Trial registration number Not applicable