Objective: A comparative study of embryo quality and pregnancy outcome between Sydney IVF medium and Quinn's Advantage sequential culture media. Design: A prospective randomised controlled trial and a retrospective study. Setting: In vitro fertilisation clinic in an academic research environment. Patients: All women < 38 years undergoing fresh embryo transfers. Interventions: Use of clinic specific age, randomisation of patients and embryo score. Main outcome measures: Fertilisation and cleavage rate, embryo quality (day 2 and day 3), blastulation rate and pregnancy rate. Results: Prospective randomised trial: In this study the only significant difference was in day 3 embryo quality (33/79 (42%) v. 40/67 (60%) for Sydney IVF and Quinn's Advantage respectively, p < 0.05). Retrospective study: Significant difference (p < 0.05) for embryo development (early-dividing embryos 156/786 (20%) v. 263/919 (29%)), day 3 good quality (234/639 (37%) v. 378/795 (48%)) and pregnancy rate (ongoing pregnancy rate 31/179 (17%) v. 59/195 (30%)) between Sydney IVF v. Quinn's Advantage sequential culture media. Conclusion: We conclude from these two studies that the range of Quinn's Advantage sequential culture media is more beneficial for in vitro embryo culture as each of the media in the range contribute collectively to more embryos with a better quality. The reason for the significant increase in embryo developmental parameters and pregnancy rate can possibly be attributed to the differences in composition between the two media.Articl