Pregnancy MaintenanceEmbryo ImplantationPregnancyPlacentaEmbryo Implantation, DelayedUterusEndometriumPregnancy, AnimalPregnancy OutcomeDeciduaEmbryo, MammalianTrophoblastsPregnancy ComplicationsPregnancy RateEmbryo TransferFertilization in VitroBlastocystPregnancy, TubalEmbryo, NonmammalianPseudopregnancyPlacentationEmbryo LossInfertility, FemaleEmbryonic DevelopmentPregnancy, EctopicChick EmbryoLeukemia Inhibitory Factor