In vitro preimplantation mouse embryo development with incubation temperatures of 37 and 39 degrees C

Embryos from two strains of mice were used to assess the effect of incubation temperature on pronuclear and two-cell development to the morula/blastocyst (M/B) stage. Embryos from B6D2F2 and B6SJLF1 strains were cultured in medium M16 at either 37 or 39 degrees C until 120 hr post human chorionic gonadotropin (hCG) or 0, 24, or 48 hr at 37 degrees C and the remaining time at 39 degrees C. Overall M/B development for pronuclear embryos was 0.6, 0, 32.3, and 52.4% for 0-96, 24-72, 48-48, and 96-0 hr at 37 and 39 degrees C, respectively. Only 0-96 and 24-72 hr at 37 and 39 degrees C were not different (P greater than 0.10). Overall M/B development for two-cell embryos was 48.1, 78.1, and 98.0% for 0-72, 24-48, and 72-0 hr at 37 and 39 degrees C, respectively. Percentage development at each time was different (P less than .01) for each category. Additionally, the number of nuclei for morulae and blastocysts tended to be higher for embryos initiating culture at the two-cell stage compared to pronuclear embryos. The first cell cycle was most dramatically affected by a 2 degrees C increase in incubator temperature. More advanced embryos can tolerate slight increases in incubator temperature more readily than pronuclear embryos.