Research question: Does splitting the human chorionic gonadotrophin (HCG) support in IVF cycles triggered by a gonadotrophin-releasing hormone agonist result in a better progesterone profile? Design: Randomized controlled three-arm study, performed at the Fertility Clinic, Odense University Hospital, Denmark. Patients with 12–25 follicles ≥12 mm were randomized into three groups: Group 1 – ovulation triggered with 6500 IU HCG; Group 2 – ovulation triggered with 0.5 mg GnRH agonist, followed by 1500 IU HCG on the day of oocyte retrieval (OCR); and Group 3 – ovulation triggered with 0.5 mg GnRH agonist, followed by 1000 IU HCG on the day of OCR and 500 IU HCG on OCR + 5. All groups received 180 mg vaginal progesterone. Progesterone concentrations were analysed in eight blood samples from each patient. Results: Sixty-nine patients completed the study. Baseline and laboratory data were comparable. Progesterone concentration peaked on OCR + 4 in Groups 1 and 2, and peaked on OCR + 6 in Group 3. On OCR + 6, the progesterone concentration in Group 2 was significantly lower compared with Groups 1 and 3 (P = 0.003 and P < 0.001, respectively). On OCR + 8, the progesterone concentration in Group 3 was significantly higher compared with the other groups (both P<0.001). Progesterone concentrations were significantly higher in Group 3 from OCR + 6 until OCR + 14 compared with the other groups (all P ≤ 0.003). Four patients developed ovarian hyperstimulation syndrome in Group 3. Conclusion: Sequential HCG support after a GnRH agonist trigger provides a better progesterone concentration in the luteal phase.