Dogs give birth to litters, meaning multiple puppies. They first come into heat and then must have sex in order to become pregnant.
A female dog comes into heat for 18 to 21 days every 6 months. Larger breeds only go into heat once a year. She will be attracted to male dogs approximately 3 to 4 days afterwards. The two dogs become stuck together during the mating process. This is called being tied together. Pregnancy in dogs lasts about 2 months. Labor in dogs is similar to human labor. The dog begins contractions before giving birth. After birth, she removes the umbilical cord.