Development of human blastocyst in dry culture system

Introduction: The most common method used to culture human embryos is inside an incubator in the presence of an atmosphere at a relative humidity close to 100% at 37°C. The purpose of high humidity is to maintain optimum osmolality of the culture medium by preventing water evaporation. In most incubators, high humidity is achieved by the use of an open tray of water. One disadvantage of the tray of water is that it increases the risk of contamination by the growth of molds, fungi or other microorganisms. This necessitates routine and time-consuming maintenance. Recently, a “dry culture system” has been designed that has no tray of water in the incubator; this reduces the risk of microbial contamination. We conducted an experiment to evaluate the clinical efficiency of dry culture system. Material and Methods: A total of 3,636 human 4- to 8-cell embryos of 1,892 IVF cycles from patients (from 26 to 40 years old) with informed consent were cultured in a dry or humid culture system. Two incubators were used to compare embryo development. The dry incubator was the EZ-Culture system manufactured by ASTEC, Japan. The conventional incubator containing a water tray was the Model AP30, also manufactured by ASTEC, Japan. Normal 4- to 8-cell embryos were cultured for 3 days from Day 2 in Blastocyst culture medium (SAGE, USA). The rates of development into blastocysts were determined on day 5. Results: Of 739 4- to 8-cell embryos cultured in the dry incubator, 423 (57.2%) developed to the blastocysts; of 2,897 embryos cultured in the humid incubator, 1,768 (61.0%) developed. There was no significant difference in the rates between the two groups. However, excellent and good blastocysts (Grade 3AA–3BB; by Gardner grading) rate of dry incubator (37.3%, 276/739) was significantly higher (P < 0.05) than those in humid incubator (16.3%, 475/2,897). Conclusions: The results suggest development of human embryos in a dry culture system was effectively identical to those of embryos cultured under standard humidified culture conditions. We conclude that it may not be necessary to use a humidified atmosphere to culture human embryos. The dry culture system used in the present study is not only efficient but also hygienic and simple to maintain. Thus, this dry incubation system seems to have advantages to reduce possible contamination as well as maintenance costs.