How can I determine if a mouse is pregnant? - briefly
Observe a rounded, enlarged abdomen and a noticeable weight gain; by days 10‑12 of gestation you can feel a soft, sponge‑like mass of embryos through gentle abdominal palpation. Absence of a vaginal opening and a lack of estrous cycling also indicate pregnancy.
How can I determine if a mouse is pregnant? - in detail
Pregnancy in a laboratory mouse can be confirmed through a combination of physical examination, behavioral observation, and diagnostic testing.
Physical signs become apparent around days 7‑10 of gestation. The abdomen may enlarge slightly, and the nipples (mammary buds) become more prominent and pink. Weight gain of 2‑3 g over a baseline of 20‑25 g often indicates conception, although normal fluctuations can mask this change. Palpation of the abdominal wall can reveal embryos after day 12; a gentle, firm pressure applied to the ventral surface should elicit a distinct, firm mass rather than soft tissue.
Behavioral cues provide additional evidence. Pregnant females typically exhibit nesting behavior, gathering bedding material and constructing a nest before parturition. They may also show reduced aggression toward cage mates and increased grooming of the ventral area.
Diagnostic tools offer definitive confirmation.
- Ultrasound imaging: High‑frequency transducers (≥30 MHz) detect fetal heartbeats and gestational sacs as early as day 8.
- Hormonal assays: Elevated serum progesterone (≥20 ng/mL) and prolactin levels correlate with pregnancy; ELISA kits provide quantitative results.
- Radiography: Soft‑tissue X‑ray can visualize fetal skeletons after day 15, useful for confirming litter size.
- Necropsy: Dissection of the uterus reveals implantation sites and embryos; this method is terminal and reserved for research endpoints.
Timing considerations are critical. The mouse gestation period lasts 19‑21 days; detection methods before day 7 are unreliable, while after day 15 physical signs become unmistakable. Combining weight monitoring with visual assessment from days 7‑10, followed by palpation or imaging from days 12‑14, yields the most accurate determination.