The duration of the gestation in dogs is 57-70 days from breeding and about 61-64 days in cats.
Abdominal palpation may detect uterine swellings between days 20-13 of gestation.
Abdominal radiography can detect fetal skeletones 42-45 days of gestation and the number of fetuses can be counted. Radiographs are also useful to predict problems at parturition (dystocia).
Transabdominal ultrasound is the most informative method to confirm pregnancy. Ultrasonography can usually detect the fetal vesicles between 16-20 days of gestation. If a definitive diagnosis cannot be made, a reevaluation may be warranted in 1-2 weeks.
The fetal heart beat and embryo can be detected via ultrasonography at days 23-25 days and fetal movement at 34-36 days.
If the time of breeding is known, pregnancy can usually be rulled out 30-33 days of breeding in dogs and 15-20 days after the last breeding in cats. based on the negative ultrasonographic examination.
No routine blood or urine tests are available for the pregnancy diagnosis in dogs.
At this time, abdominal ultrasound is the tool that establishes the diagnosis of pregnancy the earliest.
Canine and Feline Endocrinology and Reproduction, 2nd edition,Feldman and Nelson
Atlas of Small Animal Ultrasonography, 2nd Edition, Pennick and d'Anjou
Clinical Veterinary Advisor Dogs and Cats, 2nd edition, Cote