Abstract: Disclosed is a medium for the propagation of early stage embryos to blastocyst stage. The medium contains an effective amount of GM-CSF to increase the percentage of pre-blastocyst embryos which develop to transfer ready blastocysts. Also disclosed is a method of growing early stage human embryos to transfer ready blastocysts. The method includes the step of incubating the embryos in vitro in a culture medium containing an effective amount of human GM-CSF for a time and under conditions to increase the proportion of transfer ready blastocysts. An IVF program that includes the method of growing early stage human embryos to transfer ready blastocysts is also disclosed.