The effectiveness of Paraffin oil and Mineral oil for day-5 embryo culture in couples undergoing in vitro fertilisation

•Live birth rate was not different between Paraffin oil and Mineral oil for day-5 embryo culture.•Both oils resulted in comparable embryo quality.•The choice of which oil to be used might be only based on the availability and the product pricing. This study evaluated the effectiveness of Paraffin oil versus Mineral oil for day-5 embryo culture in couples undergoing assisted reproductive technology (ART). We performed a multi-centre, retrospective cohort study at IVFMD (My Duc Hospital) and IVFMD Phu Nhuan (My Duc Phu Nhuan Hospital) from January 2019 to September 2019. We studied couples treated by intracytoplasmic sperm injection (ICSI), using fresh, ejaculated semen and undergoing day-5 embryo transfer. Couples who underwent in vitro maturation (IVM) or oocyte donation cycles or couples where the woman had uterine abnormalities were excluded. From January 2019 to May 2019, we used Mineral oil (LiteOil, LifeGlobal) while Paraffin oil (Liquid Paraffin, Origio) was used from June 2019 to September 2019. The primary outcome was live birth rate after the first transfer, either from a fresh transfer or frozen embryo transfer. Between 1st January 2019 to 30th September 2019, there were 2,312 couples undergoing ART in both centres, of which 762 (377 in the Paraffin group and 385 in the Mineral group) eligible couples were included in the study. Baseline characteristics of couples were comparable between the two groups, with mean female age 31.5 ± 4.3 versus 31.9 ± 4.7 in the Paraffin and Mineral group. Live birth after the first transfer occurred in 153 (40.6%) couples in the Paraffin group, compared to 152 (39.5%) couples in the Mineral group (risk ratio 1.02, 95% confidence interval 0.91 – 1.14). Other secondary outcomes were comparable between the two groups. In day-5 embryo culture, Paraffin and Mineral oil resulted in a comparable live birth rate.