There is study of influence of transplantation of pregnant rat bone marrow cells (rBMC) or of human umbilical blood cord cells (hUBCC) on the growth of rat fetuses during pregnancy. Intravenous transplantation of rBMC or subdermal transplantation of hUBCC were made once during SD 7, 8, 9, 10, 11, 12 or 13. General view and weight of fetuses were valued at SD18. After rBMC transplantation at SD 7-9 the weight of fetuses was increased up to 835 ± 15 mg, After transplantation of rBMC at SD’s 11-12 the fetuses weight was decreased up to to 587 ± 5 mg. After hBCC transplantation at SD’s 9-10 the fetuses weight was 848 ± 8 mg. It are decreased up to 826 ± 28 and 782 ± 22 mg correspondingly on SD’s 11 and 13 transplantation. There is conclusion that transplantation of cells with stem cells properties to pregnant rats during gastrulation increase the fetuses weight at SD’s 18. At the same time, the intravenous injection of antirat, antirenal rabbit antisera (AnRAnRR antisera). AnRAnRR antisera injected once during SD’s 7-10, produced malformations of rat fetuses at SD’s 18. Teratogenic effect of AnRAnRR antisera disappeared at SD’s 11 and next days of pregnancy. Results show the possibility of regulation in vivo of fetuses growth and of retardation of growth by means of transplantation of cells with stem cells properties or by means of antirenal antisera injections correspondingly.