Puppies are born dead more often than many dog owners expect. A large cohort study covering 224 breeds found that 4.3% of all puppies are stillborn, with another 3.7% dying within the first eight days of life. The causes range from infections the mother picks up during pregnancy to oxygen deprivation during a difficult labor, genetic abnormalities, and hormonal problems that quietly undermine the pregnancy weeks before delivery.
Infections During Pregnancy
Infectious agents are the most common cause of canine abortion and stillbirth overall. Two pathogens stand out. Canine herpesvirus is widespread in the dog population and can cross the placenta to infect developing puppies, particularly during the last few weeks of gestation when the immune system of the fetuses is least equipped to fight it off. Puppies infected in the womb may be stillborn or die within days of birth.
Brucella canis, a bacterium first identified by researchers at Cornell University, is another major cause of late-term pregnancy loss. It can circulate silently in a dog with few obvious symptoms, making screening essential for breeding animals. Veterinary guidelines recommend testing breeding females every six months or before each breeding, especially if they come from high-risk populations or multi-dog facilities.
Other bacterial infections can also reach the uterus and placenta, creating inflammation that cuts off nutrient and oxygen supply to the puppies. In many of these cases, the mother herself may appear only mildly ill or show no symptoms at all.
Oxygen Deprivation During Labor
Prolonged or obstructed labor, known as dystocia, is one of the most immediate causes of stillbirth. When a puppy gets stuck in the birth canal or contractions stall for too long, the puppy’s oxygen supply through the umbilical cord is compressed or interrupted. This triggers a cascade: the puppy’s blood oxygen drops, carbon dioxide builds up, and acidosis sets in. Organs with high oxygen demand, particularly the brain and heart, begin suffering cell death. If delivery isn’t completed quickly, the damage becomes fatal.
The difference between an emergency and a planned cesarean section illustrates this dramatically. In one study, puppies delivered by elective C-section had a 99.2% survival rate, compared to 87.1% for puppies delivered by emergency C-section, where the mother was already in distress. That gap exists almost entirely because emergency cases involve puppies that have already been oxygen-deprived for some time before surgery begins.
Genetic and Developmental Defects
Some puppies are never viable. Chromosomal abnormalities that occur during fertilization or early cell division can produce embryos that develop partially but cannot survive to birth. Inherited metabolic defects can also cause fetal death or produce puppies that are alive at delivery but too compromised to survive.
One specific condition, fetal anasarca, causes severe fluid retention throughout the puppy’s body, making it disproportionately large at term. This condition appears in several breeds, and it creates a double problem: the affected puppy itself is not viable, and its swollen size can obstruct the birth canal, putting the rest of the litter at risk through prolonged labor. Single or multiple puppies within the same litter can be affected. The exact genetic mechanism varies by breed and isn’t fully understood.
Inbreeding increases the likelihood of these lethal defects by raising the chances that both parents carry the same harmful recessive genes. Breeds with small gene pools tend to have higher rates of congenital abnormalities.
Hormonal Failure
Dogs depend entirely on progesterone from the ovaries to maintain pregnancy. There is no placental takeover of hormone production like in humans. If progesterone drops too early or too far, the uterine lining can no longer support the developing puppies, and the pregnancy fails.
Veterinary guidelines have traditionally set minimum progesterone thresholds for a healthy pregnancy, recommending levels above 20 ng/mL in early and mid-pregnancy and above 5 ng/mL in late pregnancy. However, a study of 98 pregnant dogs found that more than half had progesterone levels below these cutoffs at some point, yet many still delivered healthy litters on schedule. This suggests the safe range is wider than previously thought, but a sharp or sustained drop remains a real risk factor for late-term loss.
Trauma, Drugs, and Other Physical Causes
Physical trauma to the mother’s abdomen during pregnancy can damage the placenta or directly injure developing puppies. Certain medications are also toxic to canine embryos. Some drugs that are safe for non-pregnant dogs can cause fetal malformations or death when given during pregnancy, which is why veterinarians carefully screen any medications before prescribing them to a pregnant dog.
Tumors in the uterus, though less common, can also disrupt blood flow to the placenta or physically crowd out developing puppies. Endocrine disorders beyond progesterone, such as thyroid dysfunction, can contribute to pregnancy failure as well.
Breed and Litter Size
Flat-faced breeds like Bulldogs, Pugs, and French Bulldogs are often assumed to have higher stillbirth rates because of their need for cesarean delivery. The reality is more nuanced. One study comparing brachycephalic and non-brachycephalic breeds found no significant difference in neonatal survival when both groups were delivered by C-section: 94.8% survival for flat-faced breeds versus 91.8% for other breeds. The skull and airway shape of these breeds doesn’t appear to make the puppies themselves more fragile.
What does matter is the type of C-section. Elective, planned surgeries performed before labor becomes an emergency produce far better outcomes regardless of breed. Interestingly, puppies born in larger C-section litters were also more likely to survive than those in smaller litters, possibly because very small litters sometimes indicate that some puppies were already lost earlier in the pregnancy.
Finding Out Why It Happened
When a puppy is stillborn, a veterinary post-mortem examination can often identify the cause. The most valuable piece of tissue to preserve is actually the placenta, not the puppy itself. The placenta can reveal signs of infection, inflammation, or inadequate blood flow that explain what went wrong. Ideally, the stillborn puppy, the placenta, and a blood sample from the mother should all be submitted together.
If you’re working with a veterinarian after a stillbirth, ask about having the placenta examined even if the puppy’s body isn’t sent for full necropsy. In cases where infection is suspected, identifying the specific pathogen helps protect the mother’s future litters and any other dogs in the household. For breeders dealing with repeated losses, testing for Brucella and canine herpesvirus should be a priority, along with monitoring progesterone levels throughout the next pregnancy.