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Dog Pregnancy: What To Know About Heat, Pregnancy & Prenatal Health

Dog pregnancy 101. What to know about every stage of your dog's heat cycle, how to tell if your dog is pregnant & how to care for your pregnant dog.

Aly Walansky

Updated November 21, 2022 • Published July 17, 2020

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Dog Pregnancy: What To Know About Heat, Pregnancy & Prenatal Health

The miracle of life never ceases to be fascinating and beautiful, and while we love our babies and grandbabies, we also can’t get enough of brand-new puppies. Of course, just like with human pregnancies and babies, there’s a lot of science and questions in the process, and a lot that can go right (or wrong!) if we don’t take proper care of our pet. So if your dog goes into heat, or your dog ends up pregnant, what is happening? And how do you help her?

How old are dogs when they go into heat the first time?

Much like trying to guess when a human female may start her first period, it's impossible to 100% accurately detect when the heat starts in your dog because it depends on many factors, even a dog's breed size.

“As a rule, estrous (the technical term!) starts at the age of 6-10 months when the puppy's teeth fall out,” says Claudine Sievert, a doctor of veterinary medicine and veterinary consultant.

Small breeds can go into heat at the age of 5-6 months, while dogs of large breeds can go into heat for the first time at the age of 2.

How often do dogs go into heat?

Believe it or not, this varies, too! Generally, female dogs usually can go into heat about two to three times per year. “Large breed dogs typically come into heat one to two times per year, whereas small breed dogs may come into heat two the three times per year,” says Leslie Brooks, DVM, veterinary advisor for betterpet.

Signs your dog is in heat

When they are going through a heat cycle, you may notice their vulva become enlarged and some mild bleeding from their vulva, says Dr. Brooks. They may leave spots of blood in places where they are lying down.

The good news is, many dogs are good at cleaning themselves so you may not even notice the blood. Additionally, if there are male dogs around, you may notice the male dogs being more interested in the in-heat female dog.

“Her physiological and behavioral changes will help to detect it: Dogs in heat become much more aggressive or, vice versa, very affectionate. They lose appetite, start to attack same-sex dogs, and show love towards the opposite sex,” says Dr. Sievert. As for physiological symptoms, they include urinary frequency, bloody discharge from the vulva, shedding, and "flagging," aka raising her tail to demonstrate she's available to a male dog.

The stages of a dog's heat cycle

An understanding of the four stages of a dog’s heat cycle is essential to understanding a dog’s pregnancy:


The first phase is called proestrus. “You can think of this as the time when a dog is coming into heat,” says Dr. Jennifer Coates, DVM, who serves on the advisory board for Pup Life Today. You might observe vaginal swelling and bloody discharge. Males will be interested in mating, but the female is not yet ready. Proestrus lasts for around a week, give or take a few days.


The second phase is when a dog is truly in heat, called estrus. “Vaginal swelling is evident, and discharge may be red, yellow, brown, or clear,” says Dr. Coates. The female is willing to mate during estrus, which lasts for about a week, although some dogs have significantly shorter or longer times in heat.


The third phase is diestrus, lasting around nine weeks. “If mating was successful, this is the approximate length of a canine pregnancy. Some dogs go through a pronounced pseudopregnancy during which time they can display most of the signs associated with pregnancy, including an enlarging abdomen, nesting behavior, mammary gland development, and milk production. Some even appear to go into labor,” says Dr. Coates. This occurs because a dog’s hormonal status is essentially the same during diestrus whether or not she is pregnant.


The fourth and final phase of the canine heat cycle is anestrus, a quiet period between the more hormonally active stages of estrous, says Dr. Coates. Anestrus typically lasts from three to five months but can vary between dogs.

Signs your dog is pregnant

Sometimes it is very hard to tell that your dog is pregnant, especially early on. It’s not like they can tell you, or even share what they are feeling! “Usually, you will notice that your dog is gaining weight,” says Sara Ochoa, DVM, veterinary consultant for doglab.com. “Towards the end of their pregnancy, you will notice that they have mammary development, and about 48 hours before they give birth, they will start to have milk,” says Dr. Ochoa. You may notice a few behavior changes in your dog, like nesting and becoming more territorial towards things.

The other symptoms are rather similar to women with morning sickness! “The most common signs of pregnancy in dogs are vomiting in early stages of pregnancy and her nipples becoming larger and producing a semi-clear fluid,” says Dr. Sievert.

In the later stages of pregnancy her appetite will increase, she will gain weight and her tummy will grow. You can notice the changes in her behavior as well: She may become more affectionate or grumpier and more irritable because of the physical discomfort.

How long does a dog's pregnancy last?

This varies too, just like human pregnancies, but dog pregnancy typically lasts for 63 days (about nine weeks) and can vary from 55 to 70 days.

How to make sure your dog has a healthy pregnancy

Schedule an exam with your vet

Schedule an exam with your veterinarian. They can discuss what to be prepared for when the time comes for labor so you will know if your dog needs medical help. “Your vet can also take an x-ray of your dog's belly once they are past day 45 of pregnancy to count how many puppies you should expect,” says Dr. Brooks.

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Switch to a puppy dog food formula for higher protein

As a loving and responsible pet owner, you can help your pregnant dog come through this trial. First, take care of her nutrition: “Switch her to a high-quality puppy formula just before mating, introducing it slowly over 7-10 days to avoid upsetting her stomach,” says Dr. Sievert. Make sure she stays on this new formula until she gives birth and her puppies are weaned.

Vaccinate your dog before, NOT DURING pregnancy

You want to make sure your dog is up to date on vaccines prior to them becoming pregnant to ensure the puppies have protection against parvovirus and other infectious diseases. This is a helpful guide for dog vaccinations in the first few years of life. “Once your dog is pregnant she should NOT be vaccinated as it could harm the puppies,” says Dr. Brooks. This is why they should be vaccinated before becoming pregnant.

Treat for dog parasites with pregnancy-safe products

Pregnant dogs can pass roundworms and hookworms to their unborn puppies, warned Dr. Sievert. So please take care of your mom-to-be's health, treating her with products that are safe to use during dog pregnancy.

Keep your pregnant dog exercising

And remember about physical activity. Exercise for your pregnant dog is important! “Frequent walks and light exercises will help your dog stay in shape and give birth to her puppies easier,” says Dr. Sievert.

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