Do dogs always get pregnant after mating?

Dogs do not necessarily become pregnant after mating. The necessary conditions for pregnancy are the maturation of the egg, the union of the sperm with the egg and the successful implantation of the embryo, and problems with any of these can lead to failure of pregnancy. Failure to conceive can occur if the mating period is not at the maturity of the bitch’s eggs, if the male has a reproductive disorder, if the sperm survival rate is low, or if the uterine wall of the bitch is too thin for the embryo to settle.