The female dog (dam) is only able to become pregnant during her heat cycle, which for most dams happens twice a year. Yet puppy lovers don't have to wait long once a dog becomes pregnant to see her puppies. The typical pregnancy term for dogs lasts only two months. The term begins at the point of conception and labor usually starts on day 59 to 65.
A dam becomes pregnant when she's in heat. Her heat cycle happens in two stages. During the first stage, her vulva swells and bloody discharge appears. She attracts male dogs, but pays them little attention. The first heat stage ends between days 6 and 11 and the second stage begins. She releases eggs in this stage and is fertile. Her vulva softens and the bloody discharge changes color from a light pink to a golden sand. She welcomes the attention of males for breeding.
A successful breeding process ends with the dam's eggs fertilized with the male's sperm. A fertilized egg moves into the uterus and implants. It's at this point when the dam behavior may alter either becoming more friendly or irritable. Mood swings together with swollen breasts generally occur during the third week of the pregnancy term. It's also when the embryos begin to develop. At week four, a veterinarian detects the presence of embryos and confirms pregnancy through ultra sound.
The dam's abdomen begins to grow during the fifth week. The puppies' legs and paws form. As the puppies continue to grow and develop, the dam becomes increasingly uncomfortable. She may vomit—a sign of morning sicknesses. By week six, a clear fluid discharge from the vulva is normally seen. The puppies' eyes develop, but remain closed. The seventh week marks when the dam prepares for labor (whelping). Her nipples swell. She's tired. The puppies may move about in the womb. Close to week eight, the puppies are fully developed. They position themselves for birth. The dam may dig and nest in her whelping box to prepare for the puppies arrival.
Weeks 8 and 9: Birth
The dam prepares for birth anytime during weeks eight and nine--after day 59 and before day 65. Less movement by the puppies in the womb is noticed. The dam is fidgety and unable to relax. Her temperature drops as contractions begin. Dog Breed Information Center states that pre-labor starts when her temperature drops to 97 degrees or 98 degrees, on two readings taken an hour apart.
It's sometimes difficult to determine the exact day of conception, especially when a dog has mated every 48 hours she's in heat to increase the chance of pregnancy. However, Fawavizslas.com indicates that puppies born before day 59 have less of a chance for survival.