MITOTIC-ACTIVITY DURING PREIMPLANTATION DEVELOPMENT OF HUMAN EMBRYOS

The rate of cell division of human embryos in vitro was estimated thro ughout the preimplantation period. Seventy-five human embryos were ass essed by performing nuclei counts on whole mount preparations at 24 h intervals between day 2 and day 6 of development. The results indicate that the cell doubling time increases after the first two division cy cles. The mean (+/- SEM) doubling time between day 2 and day 6 was 31 +/- 2.51 h. At the end of the designated culture periods, embryos were exposed to a microtubule disrupting agent, which caused the nuclei to arrest in metaphase. Thus, a profile of the mitotic activity at given stages of development was obtained. The numbers of actively dividing cells were frequently lower than anticipated, indicating that nuclei c ounts cannot be directly correlated with continuing mitotic activity.