Stages of Fetal Puppy Development

Canine pregnancy typically lasts 63 to 67 days from fertilization to parturition--the act of giving birth--with whelping occurring normally on Day 65, advises Dr. Vicki Meyers-Wallen of Cornell University's College of Veterinary Medicine. Fetal puppy growth happens in set stages, with veterinarians able to pinpoint specific times when the unborn puppy develops certain cells, organs and body systems. Knowing these developmental steps can help owners of pregnant canines keep the mother dog healthy while preserving the well-being of her unborn litter.

  1. Weeks One to Three

    • Puppy development begins on Day 1 when the male dog's sperm fertilizes the female bitch's ovum within the female oviducts--the tubes leading from the ovaries down to the two canine uterine horns. The first division of cells on the way to creating the puppy occurs after approximately 12 hours, with the cells remaining undifferentiated--meaning they can grow into any cell type--until they reach the eight-cell stage, reports Dr. Bretaigne Jones of the Royal Canin website. At this point, the cells start to specialize into embryonic cell types that develop later into particular cells necessary for the growing puppy.

      Once the cells reach a 16-cell mass, they become an actively growing embryo in the uterine horn. By the end of the second week of pregnancy, the embryo achieves a 64-cell mass and by Day 19 implants in the uterine wall, where it continues to grow, receive nutrients and oxygen from the newly emerging placenta, and develop into a fetus.

    Weeks Four to Six

    • By Day 30, the fetal puppy cells become committed to forming mucous membranes, digestive and respiratory glands, muscles, bone, the puppy's circulatory, genital and urinary systems, the skin and hair, the nervous system and all of the puppy's sensory organs--including the eyes, inner ear and peripheral nerves. During weeks four to six of pregnancy, the puppy's organs, bones, eyes and spinal cord begin to fully develop. The fetus starts to actually look like a dog, with whisker buds showing on its developing face, and claws and toes differentiating on the feet. By week six, the fetal puppy forms skin pigments and your vet should be able to palpate the puppy and hear a heartbeat with a stethoscope, says the Doberman Pinscher Club of America website.

    Weeks Seven to Nine

    • During the last part of the pregnancy--weeks seven to nine--the fetal puppy continues to grow inside the bitch's uterus, gaining weight and taking on nutrition from the mother. The greatest weight gain of the developing fetus occurs during these last few weeks of pregnancy, with most of the organ systems beginning to enlarge and refine themselves, and the puppies readying themselves for birth, advises Dr. Dan Rice in "The Complete Book of Dog Breeding." The puppies can be seen moving about in the mother's uterus by the naked eye and veterinary radiographs show the spinal columns and skulls of individual fetuses. Whelping typically begins by Day 63 of the pregnancy with all of the puppy's organs fully developed except the eyes, which take another one to two weeks to fully open.