How long does mouse gestation last? - briefly
The gestation period of a mouse lasts approximately 19‑21 days. Some strains may vary by a day or two.
How long does mouse gestation last? - in detail
The gestation period of a laboratory mouse averages 19 to 21 days from conception to birth. Most strains, such as C57BL/6 and BALB/c, fall within this range, although slight variations occur among different genetic lines. For example, the outbred CD‑1 mouse may complete pregnancy in as few as 18 days, while some inbred strains can extend to 22 days under optimal conditions.
During the first week, embryonic development proceeds rapidly: implantation occurs around day 4, and the embryo undergoes gastrulation and early organogenesis. By day 10, limb buds and the neural tube are visible, and the placenta reaches functional maturity. The second week is characterized by rapid fetal growth; by day 14, most major organ systems are differentiated, and the fetus begins to acquire hair and whiskers. The final days involve maturation of the respiratory and digestive systems, positioning for parturition, and preparation for suckling.
Factors that can modify the length of pregnancy include:
- Temperature: ambient temperatures below 20 °C tend to prolong gestation by 1–2 days; higher temperatures may shorten it slightly but increase risk of dystocia.
- Nutrition: caloric restriction or protein deficiency can extend gestation up to 24 days, whereas excess energy intake may reduce it by a day.
- Stress: exposure to chronic stressors, such as repeated handling or predator cues, often delays parturition.
- Parity: first‑time (primiparous) females usually have slightly longer gestations than experienced breeders.
Maternal age also influences timing. Young females (6–8 weeks) generally follow the standard 19‑day schedule, while aged breeding females (over 12 months) may experience delayed parturition and higher rates of embryonic loss.
In practice, researchers monitor gestation by checking for a copulatory plug (indicative of mating) and then counting days. Vaginal cytology can confirm estrus and ovulation, providing a more precise start point. Ultrasound imaging, typically performed on days 12–14, allows direct observation of fetal development and can verify expected timing.
Understanding the exact duration of mouse pregnancy is essential for experimental scheduling, timing of interventions, and interpretation of developmental outcomes. The narrow window of 19–21 days makes mice a valuable model for studying rapid embryogenesis and for synchronizing breeding cycles in laboratory colonies.