Does micro-drop size matter? vitrified oocyte survival is affected by the volume of warming media droplets

Currently, there are a multitude of oocyte warming protocols ranging from large volumes to micro-droplets being used in different laboratories. There are also different procedural steps ranging from use of 3 to 5 droplets with variable timing. The objective of this study was to assess whether laboratory outcomes are affected based on volume of warming media at the time of oocyte thaw. We directly compared the use of 50μl droplets to use of 200μl droplets during our standard 5 step dilution oocyte warming protocol. Retrospective study comparing laboratory outcomes using two oocyte warming micro-droplet volumes. Oocyte warming consists of a five step protocol using Irvine Scientific Vitrification Thaw media (90137, CA). We compared the laboratory outcomes of 13 cases with use of 50μl droplets to 14 cases with use of 200μl droplets. For both study arms, all oocytes were originally frozen using vitrification. The initial thawing solution used was a 2ml volume droplet at 37°C and the timing for warming was exactly the same in both groups. Micro-drop warming was performed through 5 room-temperature micro-drop dilutions of TS 1min; TS:DS 2min; DS 2min; DS:WS 2min and WS for 5min. Oocyte recovery, initial survival, 3hr survival, 2PN fertilization, cleavage and usable blastocyst rates were determined. Analysis was performed by Chi-square. Tabled 1Droplet SizeCases# Thawed% Recovered% Initial Survival% 3hr Survival% 2PN% Cleaved% Usable Blastocysts50μl1316298.274.271.763.280.738200μl1417597.791.887.77274.732.1P-value>0.05<0.0001<0.001>0.05>0.05>0.05 Open table in a new tab In the recent years there has been nearly a 5 fold increase in rate of elective fertility preservation for women. Success rates both in blastocyst formation in the laboratories as well as pregnancy outcomes has improved with the use of vitrification techniques for oocyte cryopreservation and warming. In this study we assessed whether the oocyte warming thaw protocol could affect laboratory outcomes. We demonstrated that initial survival (<0.0001) and survival after 3 hours (<0.001) were significantly improved with the 200μl droplet size. However, the rate of embryo development of the surviving oocytes in either study arm were not different for day 3 cleavage or overall usable blastocysts. These findings suggest that if an oocyte survives the warming and initial 3hr culture, they have the ability to develop equally. Size does matter, oocytes favor a larger droplet during the 5 step warming process. The 200μl study group provided the oocytes an optimal environment to recover and develop into normal embryos.