Which is the external Signs that indicate successful mating?

In the first days, it's hardly noticed, but from the fifth week, the fetuses start to grow, and the mother's abdomen may look inflated, which is more evident in females having their first litter. Simultaneously, their mammary glands start to change their shape, with an increase in size and a bright pink color, as a higher quantity of blood flows towards that zone. After, approximately, 32 days, it is possible that after touching her carefully, the veterinarian will be able to confirm that she is expecting puppies. However, some females refuse to cooperate and tighten their abdomen. At a later period, it could be difficult to distinguish the puppies from the abdominal content. A veterinarian can get ultrasound, and these can detect pregnancy within four weeks and a half. Never press her abdomen to detect if she is pregnant.

What exactly is an apparent pregnancy, and how does it happen?