Conception

• When a male dog's sperm fertilizes the eggs of an ovulating female dog, embryonic puppies begin developing in the dog's uterine horns, a pair of tubes that lead from the ovaries to the uterus, according to PetEducation.com, the website for Drs. Foster and Smith's Veterinary & Aquatic Services Department.
  
  

Early Progress

• In the first few weeks after conception, a dog may show few signs of pregnancy other than enlarged nipples, an increased appetite and more need for attention. A clear vaginal discharge after the fourth week confirms the pregnancy.
  
  

Fetal Development

• A dog's pregnancy typically lasts around 63 days. By the 28th day, a veterinarian can usually detect the fetal heartbeats through ultrasound.
  
  

Diet

• At about the fourth week of pregnancy, a dog should switch from adult dog food to puppy food. A pregnant dog may require up to four times its usual amount of food, especially as the delivery date draws near.
  
  

Activity

• A pregnant dog should get regular, non-strenuous exercise to keep up its strength and muscle tone and to avoid obesity that might otherwise result from its increased diet.