P-229 Prospective comparative study between two commercial heavy oils for culture using sibling donor oocytes collected
Authors: González-Abreu D , Rivera-Yepez A , Miret-Lucio C , Escribá-Suarez M , García-Esteve A , López-Martínez V , Benavent-Martínez M , Crespo-Simó J , Teruel-López J 
Published: June 2023

Abstract

Study question
To compare embryo development and clinical outcomes between two commercial heavy oils using sibling donor oocytes collected.

Summary answer
Our study suggests that both commercial heavy oils achieve similar embryo development and clinical outcomes rates.

What is known already
Current tendencies in IVF laboratories, such as extending the embryo culture uninterruptedly until day 6/7 or the use of dry time-lapse incubators, have enhanced the importance to use good quality oils supporting human embryo culture in vitro. The coating of the culture dishes with oil is highly important to maintain the ideal conditions that embryos need for an optimal development. Specifically, oil plays an essential role in maintaining a stable temperature, provides a barrier against external agents and contributes preventing the media evaporation, and thus, to the maintenance of an optimal pH and osmolality for the correct embryo development.

Study design, size, duration
This is a single-centre prospective study performed between February and November 2022 that included 180 donors and 213 recipients. Donors were randomized using a computer-generated randomization list. Each case was processed and cultured with a commercial single medium coated with a layer of the commercial heavy oil assigned, a mineral oil (A) or a paraffin oil (B).

Participants/materials, setting, methods
Oocytes were injected by ICSI and then cultured in 16-well dishes (EmbryoSlide+®, EmbryoScope+™,Vitrolife) prepared with each heavy oil (1700µl oil/dish). These were cultured in a time-lapse incubator (EmbryoScope+™,Vitrolife) at 37.29 ± 0.05 °C in an atmosphere of 6.5% CO2 and 5% O2. These parameters were controlled periodically (T+Button,BrightSentinel and G100,Geotech). Laboratory conditions, such as temperature, humidity and volatile organic compounds levels were monitored continuously (Octax Log&Guard™,Vitrolife) during the study period, and pH was measured in a weekly basis.

Main results and the role of chance
A total of 2554 MII oocytes were injected by ICSI (oil A, n = 1304 and oil B, n = 1250). The proportion of fertilized oocytes was identical between the two oils (A:80.00% vs B:80.53%), as well as, abnormal fertilized oocyte rate (A:6.85% vs B:5.62%) and oocyte degeneration rate post-ICSI (A:6.14% vs B:6.00%). The mean number of embryos that reached the blastocyst stage and the proportion of blastocysts suitable for clinical use (transferred or cryopreserved) was almost the same independently of the oil used (A:69.84% vs B:67.15% and A:62.39% vs B:60.71%, respectively). Statistical data analysis was performed without referring to statistical significance (p &gt; 0,05).
205 patients had an embryo transfer on day 5/6 with either fresh or cryopreserved blastocysts cultured coated with a layer of oil A (n = 101) or B (n = 104), with a mean number of 1.42 ± 0,55 and 1.33 ± 0,53 blastocysts transferred/patient in each group, respectively. No differences were found in terms of clinical pregnancy (A:69.30% vs B:67.31%) or implantation rates (A:62.37% vs B:61.53%) between both groups. Miscarriage rates were similar between group A (11.88%) and group B (12.62%).
The pH average value during the study was 7.26 ± 0.06. The mean values of the room temperature, humidity and VOCs were stable at 21.7 ± 0.4 °C, 66.7 ± 6.9% and 0.098 ± 0.01ppm, respectively.

Limitations, reasons for caution
Although heavy oils are the most competent in keeping optimal culture conditions over time, there are several culture oils with different features available in IVF market. Thus, further studies should be performed comparing among them. Future research is also needed to compare peroxidation rates of our culture oils studied.

Wider implications of the findings
The present study suggests that both commercial heavy oils used in a continuous approach may provide similar in vitro fertilization rates regarding fertilization, blastocysts suitable for clinical use or clinical pregnancy. Heavy oil features, laboratory conditions and the culture environment should be properly validated independently on each IVF center.

Trial registration number
not applicable