How Do U Know If a Dog Is Pregnant? The Advice That Does Not Hold Up

A dog is pregnant when placental tissue is present. A relaxin blood test or an ultrasound can show that; swollen nipples, nesting, clinginess, and a change in appetite cannot, because an intact female runs the same progesterone-then-prolactin sequence after every heat whether she conceived or not. Zoetis's Witness Relaxin spec sheet first lists detection from day 22 to 28 after ovulation. The Merck Veterinary Manual chapter reviewed in June 2025 by Autumn P. Davidson, DVM, MS, DACVIM, of the University of California, Davis, places ultrasonography at 25 to 35 days of gestation and warns that false-negative scans occur before day 21. Fetal heartbeats have been reported visible from 23 to 28 days of gestation. Fetal skeletons begin to calcify as early as day 28 and become visible on routine radiographs at about day 42 to 45. Late-gestation films taken after day 55 were 93 percent accurate for litter size in the 1986 University of Tennessee series by Toal, Walker, and Henry. Whelping falls 62 to 64 days after ovulation in Merck's owner chapter, 63 plus or minus 1 day after ovulation in Concannon's endocrine timing, and 58 to 71 days after a breeding date if that is all you have.

Those figures look as if they quarrel. They use different zeros for the same event, the way a yield sheet produces two official calorie totals when raw weight and cooked weight share a column.

Can nipple swelling and nesting tell you a dog is pregnant?

They cannot. They describe diestrus, the luteal phase that follows estrus in every intact bitch, pregnant or empty.

VCA Animal Hospitals (Barnes, Weir, and Ward, updated 29 April 2024) states the overlap without softening it: "Most intact female dogs show some signs of false pregnancy after estrus." The signs "usually begin four to nine weeks after the previous heat period and mimic the signs of true pregnancy," including mammary enlargement, milk, nesting, and mothering of toys.

Margaret V. Root Kustritz, DVM, PhD, a diplomate of the American College of Theriogenologists, said on Purina's breeder pages while she was professor of small animal reproduction at the University of Minnesota: "Essentially all dogs that go through estrus, or have a heat cycle, go through a false pregnancy because they undergo the same hormonal changes after estrus whether they are bred or not." When progesterone later falls and prolactin rises, milk and whelping behavior appear in the empty bitch as well. She described the visual trick: prolonged progesterone "may loosen joints, giving some dogs an abdominal distension as their ribs 'spring' apart that mimics a pregnancy appearance."

The assay that splits the two looks for a placenta. VCA's pregnancy-testing page (Williams, Ruotsalo, and Tant) writes that relaxin "is produced by the developing placenta following implantation of the embryo" and that "there is no actual placental development during pseudopregnancy, and relaxin is not produced at any time."

| What you can observe | True pregnancy | Pseudopregnancy | |---|---|---| | Relaxin in serum or plasma | Detectable once a placenta is producing it | Stays negative; no placenta | | Ultrasound | Gestational sacs, then fetal hearts | No conceptuses; uterus may be empty or diseased | | Mammary enlargement, milk | Present later in gestation | Present | | Nesting, mothering toys | Present later in gestation | Present | | Progesterone after heat | Remains high through pregnancy | Rises, then declines after four to six weeks (VCA) |

Mild false pregnancy, VCA reports, subsides in 14 to 21 days. Abdominal swelling after a heat also overlaps with pyometra, hydrometra, and mucometra, which Merck lists as the uterine-distention conditions ultrasound is used to separate from pregnancy.

Why "63 days" and "71 days" are both in print

The stable interval is ovulation to whelping.

Patrick W. Concannon, the Cornell physiologist whose LH work still sets the clinical clock, reported in Animal Reproduction in 2009 that parturition occurs 65 plus or minus 1 day after the LH surge, on average 63 days after ovulation. A 2002 JAVMA teaching case used 64 to 66 days from the LH surge and 62 to 64 days from ovulation. Merck's owner chapter, reviewed by Davidson, says the pregnancy lasts "about 62 to 64 days."

None of those sentences is dated from the afternoon she was bred. The same JAVMA case: spermatozoa persist up to 11 days, eggs remain viable up to 4 days after ovulation, "a possible gestation length from a single breeding of 58 to 71 days." LH surge, ovulation, and breeding date are different zeros. Mix them on one line and the totals disagree while both remain correct for the zero they used.

What a relaxin blood test confirms, and when it stays blank

A positive result means a placenta was present on the day the sample was drawn. It does not mean live puppies will be born, and it does not count them.

Zoetis's Witness Relaxin kit uses serum or plasma, not urine. The spec sheet, as reprinted on Drugs.com, states that implantation occurs about 18 days after the LH surge and that relaxin "is first detectable by WITNESS RELAXIN during the fourth week of pregnancy (from D22 to D28 after ovulation)." Non-pregnancy "can be certainly confirmed only starting from day 27 after bitch's ovulation."

Other official pages use other zeros. Zoetis Canada publishes "as early as 20 days post-LH surge." Texas A&M Veterinary Medical Diagnostic Laboratory (code 1206) says "as early as 22 days of pregnancy but more reliably after 28 days." Gribbles Veterinary: "by day 28 the test is positive 80% of pregnant bitches," some stay negative until day 33, protocol "Sample at 33 days after the last mating." VCA: "as early as 22-27 days post-breeding." Merck's owner chapter: "day 30 to 35 of gestation."

A 20-day claim dated from the LH surge sits about two days earlier than a 22-day claim dated from ovulation, because ovulation sits about two days after the surge. A 33-day clinic draw dated from last mating hedges a mating that missed ovulation. Zoetis lists canine sensitivity of 96.4 percent and specificity of 100 percent, citing its own technical dossier, not an independent trial.

VCA records two failure modes. Small and toy bitches carrying one or two puppies "may not produce enough relaxin to turn the test positive." A bitch can test positive and later negative, which VCA reads as pregnancy loss. Gribbles puts that drop at "within 2-3 days of the loss of a viable pregnancy."

When ultrasound confirms pregnancy, and when a heartbeat appears

Ultrasound shows whether conceptuses are there and whether they are alive.

Davidson's Merck chapter says ultrasonography is best performed at 25 to 35 days of gestation, and that false-negative results may occur before day 21. VCA places developing embryos "as early as three weeks post-breeding."

Earlier edges depend on the machine and on day zero. Cheryl Lopate, DVM, MS, DACT, in Reproduction in Domestic Animals in 2023, wrote that pregnancy can be diagnosed as early as 19 days after the LH surge as 1-millimeter spheres, "with heartbeats evident as early as 21 to 22 days in some animals, but always by day 24 post LH." Root Kustritz, in Theriogenology in 2005, collected heartbeats at 23 to 28 days of gestation and B-mode accuracy of 94 to 98 percent after 24 to 25 days. She recommended assessment "no earlier than Day 25 of gestation," because intestinal gas can hide the 19-to-20-day sacs.

What ultrasound does poorly is count. Toal, Walker, and Henry (55 bitches, Veterinary Radiology, 1986): ultrasound 94 percent accurate for pregnancy detection, 36 percent for fetal counting. Palpation in that series was 12 percent accurate for count. Root Kustritz stated the split: ultrasonography is "the preferred technique for assessment of fetal viability" and radiography "the preferred technique for assessment of litter size." The advice that does not hold up is "She has six" at the 28-day scan.

When an X-ray is useful, and how accurate the puppy count is

An X-ray is useless as an early test and useful as a late inventory.

Merck says the fetal skeleton begins to calcify as early as day 28 and is not detectable by routine radiography until approximately day 42 to 45, becoming quite prominent by day 47 to 48. Root Kustritz reported skeletons visible from 44 days of gestation.

Litter count is later. Merck: "Late gestational radiography (> 55 days) is the best method to determine litter size." Toal's series, last trimester: 100 percent for pregnancy detection, 93 percent for correct litter size. Today's Veterinary Practice tells clinicians to count heads and spines on a lateral film. Merck says fetal dentition "becomes visible at term."

The advice that does not hold up is skipping the late film because ultrasound already "counted." In Toal's head-to-head, the ultrasound count was right just over a third of the time. The radiograph, once skeletons had mineralized, was right 93 percent of the time.

What you can actually check at home

A human pregnancy test will not work. Those strips detect hCG. Canine placentas do not make hCG; they make relaxin, assayed on serum or plasma from a blood draw.

Owner palpation at three weeks fails the published numbers. Merck: uterine swellings palpable at about day 21 if the animal is cooperative. Root Kustritz: veterinary palpation window 24 to 35 days post-breeding, 87 to 88 percent for a positive diagnosis, 12 percent for litter size. After about day 35 the vesicles become confluent.

What a home record can do is preserve the denominator. Write down the first and last days she stood, any LH or progesterone dates, and the day you will request testing. Time the first relaxin or ultrasound from ovulation if you have it. If you have only a breeding window, use Merck's 25-to-35-day ultrasound band, and treat a negative relaxin as unfinished until a second sample a week later.

PetMD (Rhiannon Koehler, DVM, 21 October 2024) says that in weeks one to three "you are unlikely to notice big changes," though some bitches vomit. At three weeks the home picture is still diestrus.

FAQ

How can I check if my dog is pregnant at home?

A human urine strip will not work. It looks for hCG, which dogs do not make. Nipple swelling, nesting, and appetite shifts also appear in pseudopregnancy. The working test is a veterinary relaxin assay on serum or plasma, first listed on the Zoetis Witness sheet from day 22 to 28 after ovulation, or an ultrasound in that same window.

How do dogs act when first pregnant?

Many bitches show nothing in the first three weeks. PetMD's Koehler review says some vomit. Later, VCA lists lethargy, appetite change, clinginess or irritability, and nesting, the same behaviors VCA lists for false pregnancy. Behavior dates the luteal phase. It does not prove a placenta.

What are the signs of dog pregnancy at three weeks?

At three weeks after ovulation, Merck says uterine swellings may be palpable in a cooperative bitch, and ultrasound can begin to see sacs, with false-negatives still possible before day 21. Home signs are thin: occasional vomiting, little or no belly change. Nipple enlargement is often dated nearer day 28. Three-week "signs" are a calendar, not a diagnosis.

How soon can a dog tell if you are pregnant?

There is no published detection day, because there is no published detection study. Dr. Ann Hohenhaus of the Animal Medical Center in New York has said she suspects dogs smell something humans miss. Until a trial exists, reports of a dog changing after a human pregnancy test remain compatible with changes in the owner's gait, schedule, and mood.

When should a veterinarian use ultrasound to confirm pregnancy?

Merck, in Davidson's chapter, says ultrasonography is best at 25 to 35 days of gestation, with false-negatives before day 21. Root Kustritz reported 94 to 98 percent accuracy after 24 to 25 days. Heartbeats have been reported from 23 to 28 days of gestation; Lopate, with later machines, put some hearts at 21 to 22 days after the LH surge.

When is an X-ray useful for preparing for whelping?

After the skeletons mineralize. Merck puts radiographic visibility at about day 42 to 45 and litter-count films after day 55. Toal, Walker, and Henry found late-trimester radiography 93 percent accurate for litter size, against 36 percent for ultrasound. Count skulls and spines on a lateral film so the whelping box is stocked for the right number.