How can pregnancy in a mouse be determined? - briefly
Pregnancy is usually confirmed by detecting a copulatory plug the morning after mating and by observing a ≥2 g weight gain by day 10, with uterine palpation or serum progesterone measurement as supplemental checks. These approaches reliably identify gestation before embryos become visible.
How can pregnancy in a mouse be determined? - in detail
Detecting gestation in laboratory mice relies on a combination of physiological observation, anatomical examination, and biochemical assays.
Physical signs become apparent around days 10‑12 post‑mating. The abdomen may exhibit a slight enlargement, and the nipples (the so‑called “milk line”) become more prominent and pinkish. Palpation of the uterine horns through the abdominal wall can reveal the presence of embryos, although this technique requires experience and is less reliable in early stages.
Vaginal cytology provides a non‑invasive method. A smear taken from the vaginal opening shows a shift from predominantly leukocytes in the estrous phase to a mixture of cornified epithelial cells and leukocytes during early pregnancy, reflecting hormonal changes.
Ultrasonography offers real‑time visualization of developing conceptuses. High‑frequency transducers (≥30 MHz) can detect embryonic vesicles as early as day 7‑8, with increasing clarity of fetal structures by day 14. The procedure is performed under brief isoflurane anesthesia to minimize stress.
Serum hormone measurements complement physical assessments. Progesterone concentrations rise sharply after implantation and remain elevated throughout gestation; values above 20 ng/mL typically indicate pregnancy. Complementary assays for estradiol and luteinizing hormone help confirm the endocrine profile.
Necropsy remains the definitive confirmatory technique. Dissection of the uterine horns reveals implantation sites, decidual swelling, and embryos. This approach is reserved for terminal studies or when other methods yield ambiguous results.
In summary, reliable detection of mouse gestation combines external observation (abdominal size, nipple changes), vaginal smear analysis, high‑resolution ultrasound, hormonal profiling, and, when necessary, direct uterine inspection. Each method offers distinct temporal resolution and invasiveness, allowing researchers to select the optimal strategy for their experimental timeline.