Pregnancy is a common part of life, but there's so much mystery around it! If you've given birth or know someone who has, you might think you know a lot about conception, pregnancy and birth. It might even seem like it's similar across mammals. And while there are similarities in how different mammals give birth, there are also plenty of differences. Take dogs, for example.

If you're a dog owner or simply curious about canine pregnancy, you might wonder how dogs can get pregnant, how long they're pregnant for, and more!

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While there are similarities between dogs' reproductive systems and ours, there are many key differences you might not be familiar with.

To fully understand canine pregnancy and how it works, you'll need to know how a dog's reproductive cycle works.

Do Dogs Have Menstrual Cycles?

Female dogs don't have menstrual cycles like humans, but they do have heat cycles where they produce bloody discharge similar to a human mensuration. According to the American Kennel Club, a female dog goes into heat once every six months or so. The full heat cycle lasts somewhere between 18-21 days on average, and it's broken into four stages:

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1. Proestrus
The first stage of a dog's heat cycle lasts around 9 days. Proestrus is the part of a female dog's cycle that starts to attract males to reproduce with. This phase is marked by bloody discharge and a swelling of the vulva.

2. Estrus
The second stage of a dog's heat cycle can be short, lasting 3-4 days, though it averages around 9 days. According to the East Central Veterinary Hospital, this stage is when the female is fertile and ready to receive a male. It's characterized by a soft and enlarged vulva and lightened discharge. It's also marked by dropping estrogen levels, as progesterone levels start to rise.

3. Diestrus
The East Central Veterinary Hospital explains diestrus lasts for around two months following the estrus stage. During this phase, a dog's hormones will be responding to the heat cycle with rising progesterone levels, regardless of pregnancy or not.

4. Anestrus
Anestrus is the time between diestrus and proestrus. It typically lasts around four to six months. During this time, female dogs are not receptive to mating.

Knowing an individual dog's heat cycle better can help you determine how long a pregnancy will last.

How Long Are Dogs Pregnant For?

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According to VCA Animal Hospitals, pregnancy in dogs lasts anywhere from 57-65 days. The average canine pregnancy lasts 63 days.

The American Kennel Club notes that the gestation period (or length of pregnancy) starts from the date of conception, but that date can be hard to determine. They explain, "Sperm can live for several days inside the female, and eggs can remain fertile for up to 48 hours, which means the act of mating itself is not an exact measurement of gestation. This makes it hard to predict the length of pregnancy without the assistance of a veterinarian."

Veterinarians can offer hormone measurements to give a more precise timeline.

Stages of Pregnancy in Dogs

Much like how humans have trimesters and week measurements for pregnancy, dogs also have distinct stages of pregnancy. According to the Veterinary Healthcare Associates, the five stages of dog pregnancy are as follows:

1. Conception.
The dog goes into heat and conceives.

2. Early Pregnancy.
During the first month of pregnancy, dogs experience many symptoms similar to human pregnancy, including an increase in appetite, enlarged nipples, vaginal discharge, morning sickness, and loss of energy.

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3. Mid Pregnancy.
During the second month of pregnancy, the doggy fetuses are starting to develop from little embryos into newborn-looking puppies. The mama dog will likely gain weight and become visibly pregnant. The puppies' movement might be visible during this time.

4. Late Pregnancy.
The final stage of pregnancy in dogs only lasts a few days. It's the time when a dog prepares for labor, and she might display restless behavior and a drop in appetite.

5. Labor and Delivery.
The final stage of pregnancy involves birthing the puppies. Just like humans, dogs experience labor and contractions that help push the puppies out. The majority of puppies are delivered 30 to 60 minutes apart, though it can take longer.

Can Dogs Have Multiple Litters At Once?

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Female dogs can get pregnant with multiple male dogs and carry babies from multiple males in one litter. VCA Animal Hospitals says, "Estrus or 'heat' will continue for several...days, and [a female dog] could theoretically become pregnant from another dog during this period."

If your dog is pregnant or she might become pregnant, it's a good idea to consult with a veterinarian.