Home  /  Blog  /  Dog Pregnancy Test: Relaxin, Ultrasound, Palpation and X-Ray Explained

Dog Pregnancy Test: Relaxin, Ultrasound, Palpation and X-Ray Explained

November 10, 2026 • Admin1 • 13 min read • Dog Pregnancy
A veterinarian examining a small dog on an examination table

A human pregnancy test does not work on a dog. Human tests detect hCG, human chorionic gonadotropin, a hormone dogs do not produce. Relaxin is the only known pregnancy specific hormone in the bitch, according to Merck, and it is the hormone a dog pregnancy blood test looks for. There is no reliable at home urine test for dogs, and no human test, however sensitive, can detect a canine pregnancy. The real tests are the relaxin blood test, ultrasound, abdominal palpation and X-ray. Each works at a different time and answers a different question. Relaxin confirms pregnancy from the late third week onward. Ultrasound confirms pregnancy and viability, most reliably after day 28. Palpation may work from day 21, most reliably from day 28 to 35. X-ray cannot confirm pregnancy early at all, but after day 55 it is the best way to determine litter size.

There is no single best test for every day of pregnancy. Relaxin is simple and specific, but it cannot tell you if the puppies are alive or how many there are. Ultrasound can show heartbeats, but it cannot reliably count puppies. Palpation is quick, but it depends most on the dog and the examiner. X-ray gives the clearest count, but only after the skeletons have formed. Choosing well means matching the test to the day you are on and to the question you need answered: is she pregnant, are the puppies alive, or how many puppies are there? Use the Dog Due Date Calculator to estimate a due date once your vet has confirmed pregnancy and given you an anchor date. The calculator is an estimate. It does not confirm pregnancy and it does not replace a vet.

Why Human Pregnancy Tests Do Not Work on Dogs

Human pregnancy tests work by detecting hCG in urine. After implantation in a human pregnancy, the placenta produces hCG in rising amounts, and a home test can pick it up within days of a missed period. Dogs do not produce hCG. Their placenta produces relaxin instead. A test designed to detect hCG has nothing to detect in a pregnant dog, so it will read negative whether she is pregnant or not. A positive human test on a dog would be a false result, not a confirmation, and a negative human test tells you nothing at all. Relaxin is detected in blood, not in urine, so no human urine dipstick and no home kit can replace a blood sample sent to a vet or laboratory.

The Relaxin Blood Test

The relaxin blood test is the only blood test that confirms pregnancy in the dog. It detects relaxin, the pregnancy specific hormone produced by the placenta. A positive result means the dog is pregnant. A negative result means either that she is not pregnant, or that the test was done before relaxin had risen enough to detect. That is why timing and retesting matter. Published sources give different day ranges because they count from different points. Merck says relaxin is first detectable on day 20 to 25 after fertilisation. VCA says it is positive in most dogs 22 to 27 days after breeding. The AKC says 25 to 30 days, and the Merck owner edition says 30 to 35 days. Sperm can survive 3 to 7 days in the bitch, and dog eggs need 2 to 3 days after ovulation to mature before fertilisation, so a dog bred several days before ovulation will have a fertilisation date several days after her breeding date.

In practice, most vets plan a relaxin test for day 28 or later after breeding, and treat a negative before day 27 as inconclusive rather than final. VCA advises retesting one week later if the first test is negative. Two consecutive negatives a week apart confirm that the dog is not pregnant. Rarely, a third test is needed 31 to 34 days after breeding. A single early negative is a prompt to wait and retest, not a diagnosis. Relaxin needs only a blood sample, is not affected by body condition in the way palpation is, and distinguishes true pregnancy from false pregnancy, because pseudopregnant dogs do not produce relaxin. Progesterone cannot make that distinction, because it rises in diestrus whether a dog is pregnant or not. Relaxin cannot tell you if the puppies are alive, it cannot count puppies, and a very small litter may not produce enough relaxin for a positive result, so a negative in a small or toy breed may need ultrasound as a second method.

Dog Pregnancy Ultrasound

Ultrasound shows the puppies inside the uterus, confirms that they are alive, and can usually detect fetal heartbeats. A fetal heartbeat is evident after 25 days, so by the late fourth week a vet can often show you a heartbeat on screen. Embryos may be detectable as early as about three weeks in some cases, but ultrasound is reliably useful from 25 to 35 days, and it is most reliable after day 28. If you want to know not just whether she is pregnant, but whether the puppies are viable, ultrasound is the test to choose. It sends sound waves into the abdomen and reads the echoes. Fluid filled sacs around the embryos show up clearly, and as pregnancy advances it can show puppy movement, heartbeats and development. It does not use radiation, and it can be repeated.

The main limit of ultrasound is counting. Ultrasound does not reliably count puppies. Puppies can lie behind each other, move during the scan, or sit outside the small window the probe can see at one moment. A vet may give you an approximate number, but treat it as an estimate. If you need an accurate litter count for whelping, X-ray after day 55 is the better test. Ultrasound also depends on equipment and operator skill, and on the dog: a tense or very overweight dog may be harder to scan. A very early ultrasound, before day 25, can miss a small litter entirely, so a negative ultrasound done too early should be repeated or cross checked with relaxin rather than accepted as final. For a day by day view, see our timeline guide on how soon can you tell if a dog is pregnant.

Abdominal Palpation

Abdominal palpation is the oldest and simplest of the four tests. The vet gently feels the abdomen with their hands, looking for the small, fluid filled sacs that contain the developing puppies. It needs no blood sample, no machine and no radiation, and it can be done in a routine consultation. Palpation is possible from about day 21, and it is most reliable between days 28 and 35. Before day 28 the sacs may be too small to feel reliably. After about one month they lose their distinct shape, so palpation becomes harder again even though the pregnancy is more advanced. Accuracy depends on temperament, size, body condition, litter size and examiner experience. A relaxed, lean dog with a moderate litter is easier to palpate than a tense, overweight dog or a dog carrying a single puppy. An experienced vet will also know when not to press a doubtful finding into a false certainty.

Palpation has two hard limits. It cannot reliably confirm that the puppies are alive. Feeling a sac tells you that a structure is present, but it does not show a heartbeat or movement in the way ultrasound does. It also cannot reliably count puppies. The sacs can be hard to separate by feel, especially if there are many of them, and a count by palpation should not be used to plan whelping. If your vet feels puppies, that is a useful confirmation. If your vet feels nothing, that is not proof the dog is not pregnant, especially before day 28, after day 35, or in a tense, overweight dog or one carrying a single puppy. In that case the right next step is usually relaxin or ultrasound.

X-ray

X-ray is the last of the four tests to become useful, and the best for one specific job: counting puppies. Puppy skeletons are visible on X-ray from about day 43 to 45, when they have mineralised enough to appear on the film. Before that point an X-ray cannot confirm pregnancy or count puppies, because there is nothing dense enough to see. An X-ray at day 40 that shows no skeletons does not prove the dog is not pregnant. It proves only that the X-ray was done too early. After day 55, X-ray gives its best and most accurate litter count. The skeletons are clear, the puppies are large enough to distinguish, and the vet can count skulls and spines with confidence. That count matters at whelping. If you know there are six puppies, you know to keep watching after five have been born. X-ray can also show puppy size and position in late pregnancy. It cannot show viability in the way ultrasound can, because it shows structure, not heartbeats. Ultrasound answers the viability question in mid pregnancy. X-ray answers the count question in late pregnancy.

Comparing the Four Tests

The table below brings the four methods together so you can see at a glance which test fits which question. The earliest day is when the test may work in favourable conditions. The most reliable day is when you should plan to use it if you want a clear answer.

Test Earliest day Most reliable day What it shows What it cannot show
Relaxin blood test Day 20 to 25 after fertilisation; positive in most dogs 22 to 27 days after breeding Day 28 to 35 after breeding Confirms pregnancy; distinguishes true pregnancy from false pregnancy Viability, heartbeats, litter size, puppy position
Ultrasound Embryos detectable as early as about 3 weeks in some cases After day 28; reliably 25 to 35 days Confirms pregnancy and viability; can usually detect fetal heartbeats after 25 days Reliable litter count
Abdominal palpation About day 21 Day 28 to 35 May feel fluid sacs; quick confirmation in the right window Viability, reliable count; loses distinct shape after about one month
X-ray Skeletons visible about day 43 to 45 After day 55 for best count Best litter count; puppy size and position in late pregnancy Early confirmation; viability and heartbeats

Which Test Should You Choose, and When

If you are in the third week after breeding, ask your vet about palpation from day 21 and relaxin from day 22 to 27 after breeding, with the understanding that a negative at that stage needs a retest one week later. If you are at day 28 to 35 and you want a clear confirmation, relaxin and ultrasound are both strong choices, and ultrasound adds the viability information that relaxin cannot give. If you are past day 35 and pregnancy is already confirmed, ultrasound remains the test for checking viability, and X-ray becomes the test to plan for later if you need a count. If you are past day 55 and you need to know how many puppies to expect, book the X-ray. Gestation is 62 to 64 days from ovulation, with an average of about 63 days, and 58 to 72 days from a first mating, according to Merck and UC Davis. Cornell expresses the mating count as 63 plus or minus 7 days, and VCA gives 57 to 65 days. Breed does not change gestation from ovulation. Use the Dog Due Date Calculator with the anchor your vet confirms, and treat the result as a planning estimate.

False Pregnancy and Negative Results

False pregnancy, or pseudopregnancy, is the reason a dog can look pregnant and not be pregnant. Signs begin 4 to 9 weeks after heat and mimic true pregnancy, including nesting, mothering behaviour, milk production and abdominal enlargement in some dogs. The relaxin test is the clearest way to separate false pregnancy from true pregnancy. Pseudopregnant dogs do not produce relaxin, so a relaxin test will be negative. Progesterone cannot make the distinction, because progesterone rises in diestrus whether a dog is pregnant or not. That is why a progesterone result should never be used as a pregnancy test. If your dog shows signs of pregnancy but two relaxin tests a week apart are negative, false pregnancy is one of the explanations your vet may consider. A negative result also needs to be read in the context of litter size. Small and toy breeds with only one or two puppies may not produce enough relaxin for a positive test, even when they are pregnant. If results conflict, do not pick the result you prefer. A positive relaxin with a negative early ultrasound usually means the ultrasound was done too early and should be repeated after day 28.

What No Test Can Do

No pregnancy test can tell you the exact day your dog will whelp. Gestation ranges are wide when counted from mating, and even a precise ovulation date gives a range of 62 to 64 days, not a single day. No test can guarantee that every puppy will survive to birth, or that whelping will be uncomplicated. Ultrasound can show viability at the time of the scan, but it cannot predict the future. X-ray can count puppies in late pregnancy, but it cannot predict how labour will progress. Relaxin can confirm pregnancy, but it cannot tell you anything about the puppies themselves. Signs alone never confirm pregnancy. A change in appetite, tiredness, enlarged nipples or abdominal enlargement can suggest pregnancy, but they can also occur in false pregnancy or for other reasons, and they can be absent in a pregnant dog. This article does not give any medication, deworming or vaccine dose. Call your vet if you need to confirm pregnancy, if an early test was negative, if signs and tests disagree, or if you need a litter count before whelping. Use the Dog Heat Cycle Calculator if the mating was unplanned.

Disclaimer: This article is for general information only. The due date calculator is an estimate and does not confirm pregnancy or replace veterinary advice. Always confirm pregnancy with a vet test and follow your vet's guidance for your individual dog.

Frequently Asked Questions

How accurate is a dog pregnancy test?

A dog pregnancy test is most accurate when used at the right time. A relaxin test is accurate after day 28, and a positive result confirms pregnancy. An early negative can be wrong, especially before day 27, and should be retested one week later. Ultrasound is accurate for confirming pregnancy and viability after day 28, and X-ray is the most accurate method for counting puppies after day 55.

Can a blood test tell if a dog is pregnant?

Yes. A blood test for relaxin can confirm pregnancy in a dog. It is the only known pregnancy specific hormone in the bitch. Progesterone cannot confirm pregnancy, because it rises in diestrus whether a dog is pregnant or not.

Is ultrasound or X-ray better for confirming pregnancy?

Ultrasound is better for confirming pregnancy and viability, because it can show heartbeats and is most reliable after day 28. X-ray cannot confirm pregnancy early, because skeletons are not visible until about day 43 to 45, but it is better for counting puppies after day 55.

Can you tell if a dog is pregnant without going to the vet?

No. There is no reliable at home test for dog pregnancy. Signs alone never confirm pregnancy, and human pregnancy tests do not work on dogs, because they detect hCG, which dogs do not produce. Only a vet test confirms pregnancy.

How do vets check for pregnancy in dogs?

Vets check for pregnancy using a relaxin blood test, ultrasound, abdominal palpation or X-ray. The choice depends on the day after breeding and on the question: is she pregnant, are the puppies alive, or how many puppies are there.

What if a pregnancy test is negative but my dog still shows signs?

A negative test before day 27 after breeding does not rule out pregnancy, especially if breeding happened several days before ovulation or if the litter is small. Retest one week later. If two relaxin tests a week apart are negative, false pregnancy is one possible explanation.

Sources

Keep reading