The temporal effects of changes in in vitro fertilization culture media on the one-cell mouse embryo system

The one-cell mouse embryo system has previously been shown to be more sensitive than the two-cell system to mild changes in in vitro fertilization (IVF) culture media. To determine whether this greater sensitivity is related to the developmental stage or to the length of exposure, one-cell embryos were collected and cultured in control media (Ham's F-10, 282 mOsm/liter), in media of altered osmolality (260, 300, and 316 mOsm/liter), or in media containing Cidex diluted 1:100,000. The one-cell embryos were exposed to control or altered media in four patterns: control group--control medium for 96 hr; Group A--altered medium for the first 24 hr followed by control medium for 72 hr; Group B--control medium for the first 24 hr followed by altered medium for 72 hr; and Group C--control medium for the first 24 hr, altered medium for the next 24 hr, and control medium again for 48 hr. The percentage of embryos developing to blastocysts in Group A (exposed to adverse conditions only for the first 24 hr of culture) was significantly lower than in the control group under all conditions studied. In contrast, the percentage of blastocysts developing in Group B was significantly lower than in the control group only in medium of 315 mOsm/liter and was not different from that in controls under the other conditions studied. There was no difference between Group C and the control group. We conclude that the higher sensitivity of the one-cell system is an inherent property of the one-cell stage, as exposure of the embryo during this critical first 24-hr period proved to have the most profound consequences.