How to tell if a rat is pregnant? - briefly
A pregnant rat shows a noticeably enlarged abdomen, swollen and pinkish nipples, and often exhibits nesting behavior. These physical and behavioral changes typically emerge around the second week of gestation and continue until delivery.
How to tell if a rat is pregnant? - in detail
Pregnancy in a rat can be recognized through a combination of physical, behavioral, and diagnostic indicators.
Physical changes become apparent around the second week after mating. The abdomen enlarges uniformly, often described as a rounded, balloon‑like appearance. Nipple buds (the “milk lines”) develop and may turn pink or reddish; they become more prominent as gestation progresses. Weight gain of 30–50 g over a baseline adult weight is typical, though rapid increases may signal other health issues.
Behavioral alterations also provide clues. Pregnant females often construct nests, gathering soft material such as paper or cloth. They may become more territorial, displaying increased aggression toward other rodents, or conversely show heightened docility when handled. Feeding frequency may rise, especially during the final days before parturition.
Diagnostic methods add certainty. Gentle abdominal palpation, performed after the fourth day post‑mating, can reveal the presence of embryos as small, firm masses. Ultrasound imaging, using a high‑frequency transducer, identifies fetal hearts and organ development from day 10 onward. Blood assays measuring serum progesterone levels above the normal female range confirm gestation, though such testing requires laboratory support.
Timing considerations are essential. The gestation period for a typical laboratory rat averages 21–23 days. Detecting pregnancy before day 10 is unreliable; most observable signs emerge between days 12 and 15. Observing a litter of pups within this window validates the diagnosis.
In practice, combine visual assessment of abdominal shape and nipple development, monitor nesting and feeding behavior, and, when needed, employ palpation or imaging to achieve an accurate determination.