Advanced technology provides us with a view inside the hidden world of how puppies develop in the womb. All puppies have a gestation period of about 63 days whether they end up being as tiny as a Chihuahua or as large as a Great Dane. During that time, they grow from about the size of a pea to a puppy ready to be born.
A segment of the National Geographic documentary, "Animals in the Womb" chronicles the development of nine golden retriever puppies through gestation and birth. Using advanced ultrasound technology, three-dimensional images of puppy fetuses were captured in real time. Small cameras and life-like computer simulations were used to illustrate how the puppies appear as they develop.
All puppies start off in their own protective membrane and are barely visible even after 20 days. At that time, a puppy is still as small as a pea in a pod.
While approaching about 30 days, the embryos are only about an inch long. After a month has passed, a puppy’s heart begins to beat and her limbs and tail begin taking shape.
At this stage, her paws look more like a duck's webbed foot, as the claws have yet to form. Tiny bumps appear on either side of the mouth, marking the spots where whiskers will soon grow.
The soon-to-be puppies now enter a period of rapid development, as they have about one more month before they are born.
A puppy officially turns from an embryo into a fetus at 39 days. At this time, his legs begin small bouncing movements that help develop his muscles and strengthen the joints he will use in life.
The puppies are bald, as their fur coats have yet to grow in. Tiny ears are coming into view. Ears shapes vary widely among the different breeds of dogs. They can droop, stand up or fold over into the shape of a neat triangle.
Eyelids have formed a protective covering over her eyes, which will remain closed until one to two weeks after she is born.
Less than three weeks before birth, a puppy grows his fur coat and claws. His nose is also being defined, representing the dog's highly attuned sense of smell. Inwardly, the puppy is developing approximately 200 million scent receptors in his nose. In comparison, a human nose has approximately 5 million receptors.
After 55 days in the womb, a puppy is entering the final stages of development. Characteristics of the puppy’s breed become more defined, such as the folded and flopping skin of a bullmastiff or the long, droopy ears of a basset hound.
As the birth date approaches at about 63 days, puppies become more active in the womb. They wiggle around and their paw kicks can be seen outwardly in the mother’s abdomen area.
Ultrasound images of puppies at this stage show them panting and moving their legs as if running. They almost appear to be practicing skills they will use later on in life while running at the dog park or romping around in the backyard.