Association between trigger-intrauterine insemination interval, ovulation trigger agent, and clinical pregnancy in intrauterine insemination cycles: a 300-case analysis

Background: Intrauterine insemination (IUI) is a commonly employed first-line treatment for couples with unexplained infertility and mild male factor infertility due to its simplicity, low cost, and minimal invasiveness. Ovulation is typically induced using pharmacological triggers to allow accurate scheduling of IUI either with human chorionic gonadotropin (hCG) or gonadotropin-releasing hormone (GnRH) agonists. While insemination is commonly performed between 24 and 40 hours after the trigger, studies have reported variable pregnancy rates across different timing intervals, and no universal consensus has been established. Given these uncertainties, further evaluation of both the timing of insemination and the choice of ovulation trigger is warranted. Hence this study aims to assess how the interval between ovulation trigger and IUI influences clinical pregnancy outcomes, and to compare pregnancy rates between cycles using a GnRH agonist versus hCG as the trigger. Methods: A retrospective analysis was conducted on 300 IUI cycles performed at Janani Fertility Centre, Trichy, Tamil Nadu. Eligible cases included couples with unexplained infertility, male partners aged 23–40 years, and female partners aged 22–38 years with bilaterally patent fallopian tubes. Cycles with abnormal semen parameters, incomplete or frozen samples, double IUI, or donor sperm use were excluded. Patients were grouped according to the interval between trigger administration and IUI: <36 hours (group A, n=70), 36–38 hours (group B, n=140), and >38 hours (group C, n=90). Trigger type was hCG (n=187) or GnRH agonist (n=113). Categorical variables were analyzed using the Chi-square test. Results: Clinical pregnancy rates differed significantly across timing groups: group A: 8.6%, group B: 25.7%, and group C: 15.6%. The highest pregnancy rate occurred when IUI was performed 36–38 hours after the ovulation trigger. Trigger comparison showed higher pregnancy rates with hCG (25%; 47/187) than with GnRH agonist (8%; 9/113). Conclusions: IUI performed 36–38 hours after ovulation trigger is associated with the highest likelihood of clinical pregnancy, indicating optimal synchronization of ovulation and insemination at this interval. Additionally, hCG appears more effective than GnRH agonist as a trigger for improving pregnancy outcomes in IUI cycles.