How many days is a mouse pregnant? - briefly
A mouse’s gestation period lasts roughly 19–21 days, with most litters born after about 20 days.
How many days is a mouse pregnant? - in detail
The gestation period of a typical laboratory mouse (Mus musculus) lasts approximately 19 to 21 days, with a median of 20 days. This interval is measured from the moment of conception to the birth of the litter.
Key factors influencing the duration include:
- Strain differences: some inbred strains may complete gestation in as few as 18 days, while outbred stocks can require up to 22 days.
- Environmental conditions: ambient temperature around 20–22 °C and a photoperiod of 12 h light/12 h dark support the standard timeline; extreme temperatures or irregular lighting can extend or shorten it.
- Maternal age and health: young or aged females, as well as those experiencing nutritional deficiencies, may exhibit slight deviations from the typical range.
During the gestational phase, embryonic development proceeds through well‑defined stages:
- Pre‑implantation (Days 0–4): fertilized ova travel through the oviduct, undergo cleavage, and reach the blastocyst stage.
- Implantation (Days 4–6): blastocysts embed in the uterine lining, establishing maternal‑fetal contact.
- Organogenesis (Days 6–14): primary organ systems form; limb buds, neural tube, and heart begin functioning.
- Fetal growth (Days 14–20): rapid increase in size, maturation of lungs, and preparation for parturition.
At the end of the 19‑ to 21‑day window, the dam typically gives birth to a litter ranging from 4 to 12 pups, depending on strain and parity. The short gestation enables mouse colonies to be expanded rapidly for research purposes.