Insulin-like growth factor I (IGF-I) has been shown to increase the proportion of embryos forming blastocysts and the number of inner cell mass cells in human and other mammalian preimplantation embryos. Here we examined whether the increased cell number resulted from increased cell division or decreased cell death.

Normally fertilized, Day 2 human embryos of good morphology were cultured to Day 6 in glucose-free Earle's balanced salt solution supplemented with 1 mM glutamine, with (n = 42) and without (n = 45) 1.7 nM IGF-I. Apoptotic cells in Day 6 blastocysts were identified using terminal deoxynucleotidyl dUTP terminal transferase (TUNEL) labeling to detect DNA fragmentation and 4’-6-diamidino-2-phenylindole (DAPI) counterstain to evaluate nuclear morphology. The number of nuclei and extent of DNA and nuclear fragmentation was assessed using laser scanning confocal microscopy.

IGF-I significantly increased the proportion of embryos developing to the blastocyst stage from 49% (control) to 74% ( IGF-I) (P < 0.05). IGF-I also significantly decreased the mean proportion of apoptotic nuclei from 16.3 ± 2.9% (–IGF-I) to 8.7 ± 1.4% ( IGF-I) (P < 0.05). The total number of cells remained similar between both groups (61.7 ± 4.6 with IGF-I; 54.5 ± 5.1 without IGF-I). The increased number of blastocysts combined with reduced cell death suggests that IGF-I is rescuing embryos in vitro which would otherwise arrest and acting as a survival factor during preimplantation human development.