Are you pregnant… or just feeling “weird”? 🤔

Pregnancy under the microscope: A practical guide without scares

It is not always obvious in the first few weeks whether your dog or cat is pregnant. At first, the physical signs are usually subtle: slight weight gain, changes in appetite or calmer behaviour. These signs can go unnoticed or be easily confused with pseudopregnancy, especially in unspayed animals.

Therefore, it is not advisable to wait until the pregnancy is “noticeable”. An early veterinary diagnosis is essential, both to ensure proper monitoring if you wish to carry the pregnancy to term, and to make responsible decisions if you do not want a litter. The sooner the condition is confirmed, the more options there are for planning appropriate medical, surgical or nutritional intervention.

In addition, rigorous clinical monitoring allows for the early detection of possible complications, such as embryonic resorption, multiple pregnancies, non-viable foetuses or developmental problems. Accompanying your pet with the support of the veterinary team from the outset is an act of prevention, empathy and commitment to their well-being.

Practical guide to diagnosing, estimating the duration and monitoring pregnancy in dogs and cats

Knowing whether your dog or cat is pregnant is not always obvious during the first few weeks: the external signs can be subtle and misleading. A slight weight gain, changes in appetite, more hours of sleep or calmer behaviour may appear… but these can also occur in other normal hormonal situations. In unspayed females, some of these changes can easily be confused with pseudopregnancy, also known as psychological pregnancy, a phenomenon described in up to 50–75% of intact bitches throughout their reproductive life. Therefore, relying solely on observation at home often leads to errors.

To avoid subjective interpretations, a simple method is very useful: for 7–10 days, note down appetite, activity and bowel movements daily, and check weight once a week. In clinical reproductive follow-up studies, weight variations of more than 5% in less than two weeks without dietary changes are considered relevant data that justify veterinary examination.

In veterinary medicine, early confirmation of pregnancy is not just for the sake of “knowing”. It allows for proper planning if the pregnancy is to be carried to term, or for responsible decisions to be made if a litter is not desired. The sooner the actual reproductive status is confirmed, the greater the scope for action and the safer the options available. In reproductive protocols, early diagnosis is considered to be that performed before day 30 post-copulation, as it significantly reduces the risk of late interventions and associated complications.

In addition, early monitoring reduces the risk of unpleasant surprises. Early embryonic resorption, described in both dogs and cats, can affect part of the litter without obvious external signs and has been observed in serial ultrasound studies in up to 20–30% of early pregnancies, especially in young females or those under stress. Simply put, a pregnancy may appear normal… until it is no longer so.

Your vet advises📝 “If there was a possible mating, write down the dates as if you were a detective.”

Recording the days of oestrus, possible matings or even doubtful situations greatly helps in choosing the right time for diagnostic tests. In reproduction, a few days’ difference can explain why an ultrasound scan ‘sees nothing’ today and sees everything a week later. 

Confirm it with science (and not with hope): how it is really diagnosed

The diagnosis of pregnancy must be made at the veterinary clinic and is usually supported by several complementary tools, each with its optimal timing and specific usefulness. From a practical point of view, not all tests are equally reliable at all stages of pregnancy.

Abdominal palpation can be performed approximately 25 days after mating. In experienced hands, its sensitivity is around 60–75%, but it decreases markedly in small litters, in overweight animals or when performed too early. Therefore, a negative palpation should never be considered definitive.

Ultrasound is currently the technique of choice for early diagnosis. It allows confirmation of pregnancy, observation of the heartbeat and assessment of embryonic viability, i.e. the embryo’s ability to continue developing. In dogs, the heartbeat is usually detected between days 22 and 25, while in cats it can be observed even earlier, around days 16–18, depending on the equipment and the experience of the examiner. Comparative studies show that ultrasound performed between days 25 and 30 has a sensitivity of over 95% for confirming pregnancy. In a study using ultrasound in bitches, diagnostic accuracy reached approximately 94% from day 24, 98% from day 25 and 99% around day 28, which explains why ‘too early’ is one of the most common causes of confusing results.

In addition, ultrasound allows non-progressive pregnancies to be identified. In serial follow-ups, it has been reported that embryos with no detectable heartbeat in repeated checks have a very high probability of not reaching full term, allowing follow-up to be adapted and possible uterine complications to be anticipated.

Did you know 🔍: “Seeing ‘something’ too early can be worse than seeing nothing.”

It has been reported that very early vesicles can be seen around days 19–20, but they may be obscured by intestinal gas; therefore, many authors recommend not evaluating “too early” and repeating at the optimal window. 

The relaxin hormone test is another useful tool, especially in female dogs. Relaxin is a hormone produced by the placenta, and its detection in blood confirms the presence of functional placental tissue. In clinical studies, relaxin begins to be reliably detected from day 20–25, reaching a sensitivity of nearly 100% from day 28–30. An early negative result does not rule out pregnancy, but a correctly interpreted positive result is highly specific. In a clinical study with cats using a commercial relaxin test (originally designed for dogs), pregnancy was detected as early as day 20, and its sensitivity reached 100% from day 29 onwards; a specificity of 95.9% was also reported due to some false positives associated with ovarian cysts, bearing in mind that interpretation must always be clinical and contextual.

Radiography is not used to confirm early pregnancies, but it is essential in advanced stages. From day 45 onwards, foetal mineralisation allows the number of foetuses to be counted fairly accurately. In studies on labour management, knowing the exact number significantly reduces the risk of undetected foetal retention and is associated with a decrease in obstetric complications. A recent clinical review on pregnancy/labour monitoring in dogs highlights that radiographs are particularly useful for foetal counting when performed approximately between days 57–65, helping to minimise the risk of “missing” an already mineralised foetus in the final stage.

An often underestimated aspect is that the combination of early ultrasound and late X-ray provides the most comprehensive information: viability, evolution and safe delivery planning.

How long does gestation last? The realistic timeline

In dogs, the average duration of gestation is around 63 days, with a typical range of 58 to 65 days. In cats, the duration usually ranges from 58 to 67 days. These figures come from large clinical series and reflect normal biological variability.

This variability depends on multiple factors: breed, body size, number of foetuses and exact time of ovulation. For example, in large litters there has been a slight tendency towards slightly earlier births, while pregnancies with one or two foetuses may be prolonged without this implying any pathology. HERE 5 (in foetal biometry studies, it is emphasised that breed-specific morphology —and not just weight or size— can influence ultrasound measurements and, therefore, the estimation of gestational age, which explains why two females may “measure differently” even though they are equally pregnant).

From a practical point of view, it is more useful to work with “intervals” than with exact dates. In the final stretch, preparing the environment in advance reduces stress, a factor that has been linked in behavioural studies to an increase in functional dystocia.

Smart monitoring: key care during pregnancy and warning signs

Proper monitoring combines regular veterinary check-ups, nutritional adjustments and careful observation at home. Although most pregnancies progress normally, when complications arise, they tend to do so gradually and discreetly.

Nutrition is especially critical in the last third of gestation. In bitches, foetal growth accounts for approximately 70% of total weight gain, concentrated in the last 3–4 weeks. Nutritional studies indicate that energy requirements may increase by 30–60% compared to maintenance, depending on litter size. For this reason, a high-energy, highly digestible diet, divided into several daily meals, is recommended. Dividing the ration reduces vomiting and improves digestive tolerance, something that has been consistently observed in clinical studies.

Uncontrolled supplementation, especially with calcium, is not harmless. It has been shown that excess calcium during pregnancy can alter the hormonal mechanisms of labour and increase the risk of puerperal hypocalcaemia, a potentially serious emergency.

As for medication and deworming, any drug should be carefully evaluated during pregnancy. Some antiparasitic drugs are safe and others are contraindicated, and their use should be based on specific protocols. Veterinary pharmacovigilance studies emphasise that many adverse foetal effects are related to unnecessary or inappropriate administration.

Moderate physical activity contributes to well-being and muscle tone. Excessive sedentary behaviour has been associated with an increased risk of gestational overweight and longer deliveries, while intense exercise or heat stress increases the risk of complications. Balance is key.

There are warning signs that warrant immediate consultation: abnormal vaginal discharge, fever, marked weakness, abdominal pain, persistent vomiting, or labour without progress. In veterinary obstetric studies, early intervention in response to these signs is associated with better neonatal survival rates and lower maternal morbidity.

Final key idea

An undiagnosed or improperly monitored pregnancy can progress without obvious signs until it becomes an emergency. Veterinary supervision based on objective data, scheduled check-ups and informed observation is not an excess of caution: it is a prevention strategy that has been proven to improve the safety of the mother and the litter.

Full references and recommended reading

Zambelli, D., Prati, F., Cunto, M. (2004) – Diagnostic accuracy of ultrasound in early pregnancy in dogs. – Journal of Veterinary Medicine (Redalyc) – Clinical study demonstrating that ultrasound achieves an approximate diagnostic accuracy of 94% from day 24, 98% from day 25 and 99% around day 28 of gestation, explaining the high rate of false negatives when performed too early. –

Hoffmann, B., Riesenbeck, A., Klein, R. (2011) – Use of the hormone relaxin for pregnancy diagnosis in domestic cats. – Theriogenology – Study evaluating a relaxin test demonstrating pregnancy detection from day 20 and 100% sensitivity from day 29, with high specificity and rare false positives associated with ovarian pathology. –

Davidson, A. P. (2023) – Monitoring pregnancy and planning delivery in dogs. – Clinical Theriogenology – Clinical review highlighting the usefulness of radiography in advanced stages of pregnancy (approx. days 57–65) as a reference method for foetal counting and the prevention of undetected foetal retention. –

Luvoni, G. C., Grioni, A., Ferré-Dolcet, L. (2014) – Ultrasound foetal biometry and racial variability in dogs. – Animal Reproduction Science – Study demonstrating that breed-specific morphology influences ultrasound foetal measurements and gestational age estimation, beyond body weight or size. –