Watching a mother dog bring new puppies into the world is an exciting experience. However, not every puppy lives through the process. In fact, it's not uncommon that one or two pups are stillborn during birth. There are many reasons a puppy could be born dead, including those relating to its size, position in the birth canal and infections in its mother.
Pelvic Canal Obstruction
One reason a puppy can be born dead is that it was too big to easily fit through the birth canal and got stuck during delivery. This problem is called pelvic canal obstruction. While the mother is struggling to push out the puppy, the water sac holding it in the womb and giving it oxygen might break. Without the sac, the puppy could drown. Some breeds are more at risk for pelvic canal obstruction during birth, including dogs with large heads such as English Bulldogs, Pekinese and Boston Terriers.
If a puppy becomes breech during the birthing process, it could be born dead. Breech puppies get turned around during the birth; instead of coming out of the womb and vagina headfirst, they are trying to be pushed out sideways or back legs first. Breech puppies that aren't pushed (or pulled out by a helper) within two to 10 minutes could have their umbilical cord pinched or their water sac ripped -- either of which could cause it to drown.
A stillborn puppy might have fallen victim to a bacterial infection while the mother was pregnant. There are an array of bacterial infections affecting dogs that can cause spontaneous abortions and stillborn puppies, including brucellosis. This bacterial infection can be transmitted during mating and can cause a pregnant dog's puppies to be spontaneously aborted in the third trimester. Canine herpesvirus infection, toxoplasmosis, mycoplasma and ureaplasma are other bacterial infections that can kill puppies and lead to stillbirths.
There are an array of miscellaneous causes that might lead to a stillborn puppy. The dog could have had a genetic defect, or the foetus might have suffered nutritional deficiencies while in the womb. Although stillbirths are not uncommon in dogs, determining the cause might not be possible without an autopsy and chromosomal analysis of the body. If you want to find out the cause of your puppy's death, save the body after it's born. Put it and its water sac in the refrigerator (don't freeze it) and call your veterinarian for more instructions.