While human pregnancy lasts nine months, the normal gestation period in dogs is only nine weeks. Over this 63-day period, the female dog experiences physical and behavioral changes as puppies develop and she prepares to become a mother. The pregnancy development is much faster than in humans, and the female dog will show changes to her body around the fourth week.
The dog gestation period is much shorter than human pregnancy, and changes happen quickly in the dog's body. During the first and second week following successful mating, eggs are fertilized and travel to the uterus to develop. By the third week, embryos begin to grow, and puppy fetuses can be visible through ultrasound by week four. The dog's abdomen begins to swell at around the fifth week of pregnancy, which is when the dog is visibly pregnant. Because of the speed of development, it can be difficult to determine if a dog is pregnant until the fourth or fifth week of gestation.
As the pregnancy continues into its final weeks, puppies continue growth and development in the womb. By week eight, the puppies are almost fully formed and the mother may prepare by looking for a comfortable place to give birth. During the last two weeks, owners should prepare an area for the mother to deliver, although, when the time comes, she may prefer privacy and deliver in an unusual location, such as in a closet or under a bed.
Some dogs experience morning sickness around the third week of pregnancy, but the nausea is not always accompanied by vomiting. By mid-pregnancy, the dog's appetite increases and most physical changes occur. Nipples will become larger and darker and may secrete fluid. As the dog's belly grows, she may need to urinate more frequently.
A dog's behavior may change during the last few weeks of pregnancy. Some dogs may become restless as they await delivery. Fatigue is also common. Collection and destruction of items, such as blankets, pillows and newspaper, is common because the dog wants to create a nest where she can deliver her puppies. During the final weeks of pregnancy, the dog may become irritable due to the discomfort.
Even if a female dog has an unsuccessful mating experience, her reproductive cycle may convince her that she is pregnant. These false pregnancies sometimes occur about eight or nine weeks after a mating incidence. The dog might exhibit behavior changes associated with the final weeks of pregnancy, such as nesting or milk production. The false pregnancy experience is not harmful to the dog and usually only lasts for a few days.