Preimplantation access to maternal insulin and albumin increases fetal growth rate in mice

Provision of the maternal factors, albumin and/or insulin to embryos in vitro restores preimplantation morphological development and cell proliferation to that seen in vivo. The hypothesis that the preimplantation effects of insulin or albumin would be reflected in increased fetal growth rate was examined. Two-cell embryos were cultured 48-50 h in medium supplemented with 0.17 micromol/l, 15 micromol/l albumin or 0.17 micromol/l insulin and the resultant blastocysts transferred to pseudopregnant recipients. Fetal and placental mass and skeletal development were determined at E19 or E20 (day 19 or 20 of embryonic development). Preimplantation access to insulin or albumin increased fetal growth by 4-6%. Combining insulin and albumin did not produce a further increment in fetal growth. The fetal growth achieved by providing preimplantation access to insulin, albumin or both was equivalent to that of in-vivo developed blastocysts. The conclusions are that: (i) preimplantation access to maternal insulin and albumin is required for normal fetal growth rates in the mouse and (ii) the increments in inner cell mass cell number and metabolic rates induced by insulin (and possibly albumin) reflect a requirement for maternal growth factors during preimplantation stages to optimize fetal development.