I think I bought a pregnant mouse, what do I do?

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It happens to almost anyone who buys a female mouse from a pet shop, and it’s a risk you need to accept if you choose to go that route. Pet shops are notorious for not separating boys and girls, either accidentally or because they don’t particularly care. I’ve even come across more than one pet shop who purposely leave boys and girls together so that any female mice they sold would have babies to be returned to their shop as more stock.

If you’re concerned about your mouse being pregnant, there are some things to check for.

  • Double check the sexes of your mice. The shop may or may not have sexed them correctly. See sexing pictures further down this page.
  • If you find you have mixed sexes, you need to make the decision to return one sex, or separate them into same-sex cages (remove the male ASAP regardless, on the chance that he hasn’t gotten her pregnant yet). You cannot keep males and females together for the long run because they will breed constantly (ie. a litter every 3 weeks). This is not only incredibly taxing on the poor girl, but you will have a lot of babies to find homes for.
  • If you definitely have only girls, then the next step is to wait 19 – 21 days, which is the gestation period of a mouse. If the 21 day mark passes, no babies for you!
  • However, if your mouse starts to look like she swallowed a golf ball (mice only start to show physical signs of pregnancy at about 2 weeks) you might soon have a litter on your hands.
  • Note, that many females will get pregnant at the pet shop so even if you do have only girls, you might still end up with a litter.