The oil overlay in microdrop culture systems prevents medium evaporation, helps to maintain appropriate pH and osmotic conditions and protects from microbial contamination. In the present study, we prospectively compared covering by Ovoil™, a paraffin oil, and LiteOil, a mineral oil, on the in vitro development of human embryos and their suitability for transfer/freezing at day 3 and live birth rate. One hundred and one patients undergoing In Vitro Fertilization (IVF) treatment by Intracytoplasmic Sperm Injection (ICSI) were enrolled in our study. After ICSI, 1237 oocytes were 1:1 randomly allocated into 2 groups according to the type of overlaying oil: Ovoil™ (616 oocytes) or LiteOil (621 oocytes). Fertilization rate was assessed around 18 hours post-insemination (hpi) and embryos were checked for early cleavage at 25 hpi. Embryo morphology was recorded on days 2 and 3. A total of 437 and 438 day 3 embryos were analyzed. There were no differences between the two groups in terms of fertilization rate and occurrence of early cleavage. The proportion of top-quality embryos (41.7% vs. 41.2%) and the final utilization rates (92.2% vs. 92.0%) were similar in Ovoil and LiteOil groups, respectively, at day 3. Live birth rate per transfer was essentially the same with Ovoil™ overlay (26.9%) when compared to LiteOil (26.2%). Live birth rate in patients who simultaneously received embryos from both overlay types was 17.2%. Despite the different characteristics of these two oils regarding hydrocarbon saturation, packing and temperature storage, Ovoil and LiteOil can be used in parallel in the same IVF protocol.
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