OBJECTIVE To evaluate the association of timing of hCG administration and probability of pregnancy in patients stimulated with recombinant FSH/GnRH antagonists for IVF. METHODS Prospective randomized controlled clinical trial. METHODS Dutch-speaking Free University of Brussels. METHODS One hundred twenty patients, aged <40 years, treated by IVF or intracytoplasmic sperm injection. METHODS Ovarian stimulation was achieved using recombinant FSH starting on day 2 of the menstrual cycle at a fixed dose. To inhibit premature LH surge, daily GnRH antagonist was used from day 6 of stimulation. Triggering of final oocyte maturation was performed using 10,000 IU of hCG. Patients were randomized to receive hCG either as soon as three or more follicles of size ≥16 mm were present on ultrasonography (early-hCG group) or 1 day after the above criterion was met (late-hCG group). METHODS Ongoing pregnancy rate. RESULTS Significant differences were observed between the early-hCG and the late-hCG group regarding E(2) (1,388 ± 931 [mean ± SD] vs. 2,040 ± 1,231 pg/mL, respectively) and P (0.8 ± 0.3 vs. 1.1 ± 0.5 ng/mL, respectively) levels on the day of hCG administration and the number of metaphase II oocytes (9.2 ± 7.1 vs. 6.1 ± 4.9, respectively). No significant differences were observed between the early-hCG and the late-hCG group regarding positive hCG (46.2% vs. 50%, respectively) and ongoing pregnancy rates (34.6% vs. 40.7%, respectively). CONCLUSIONS The current study provides evidence that earlier administration of hCG is not associated with the probability of pregnancy in cycles stimulated with recombinant FSH and GnRH antagonists.