a, Percentages of pups from 2-cell embryos transferred. The numbers of pups obtained from 3 independent embryo transfer experiments are shown. b, Fertilization and preimplantation development. Eggs with pronucleus/pronuclei (PN) (left), the number of PN (middle) and early embryonic development in culture (right). The mean values ± s.d. from 5 biological replicates are shown. The total numbers of oocytes/embryos are shown in each graph. c, A uterus at 10 days after transfer of embryos from ESC-derived oocytes. White arrowheads indicate degenerating conceptuses that had decidua without any apparent embryo, and therefore embryo loss at early gestation. The table below the image summarizes the numbers of remaining embryos and decidua without embryo observed at 10 days of gestation. On average, 3.7 embryos remained in the uterus. Scale bar, 5 mm. d, Embryos collected from a day 10 uterus after transfer of embryos from ESC-derived oocytes. The developmental stage of the embryos was varied. Scale bar, 2 mm. e, Implantation marks in the uterus on Caesarean section. White arrowheads indicate the implantation marks without embryos and the asterisk shows the uterus wall after delivering newborn pups by Caesarean section. The table below the image summarizes the numbers of pups and implantation marks without embryos on Caesarean section. On average, 2 pups were obtained per uterus, indicating there was some amount of embryo loss during late gestation.