The average canine pregnancy lasts approximately 64 to 66 days. During the first two-thirds of her pregnancy, keep the dog on her normal maintenance diet. The fetus will grow most rapidly during the third trimester; this is when the mother needs a higher-calorie diet (calories and nutrients should be 1 1/2 times greater than the maintenance diet). Do not add supplements or medications unless advised by your veterinarian. Pregnancy diagnosis is usually first reliable around 18 to 19 days of gestation.
For more information, please see the story Pregnancy, Birthing and Newborn Puppy Care