Mouse Pregnancy Stages

Considerations

• Most pet mice should not be bred and most pet mouse owners should not attempt breeding the mice. Only mice who are superior in health and temperament should be bred. Mice used for breeding should also have at least a five-generation pedigree showing a family history of good health.
  Owners considering breeding their mice should consider the risk of losing the mother and all the babies. Even if pregnancy and delivery go well, the problem of finding homes for the babies remains. It is difficult to find adopters who will care for their adopted mice for life.

Mating

• Bucks (male mice) and does (female mice) should be introduced in a cage that is not either mouse's full-time home. This will help to avoid territorial disputes. Most bucks and does will become friendly to one another immediately or will at least tolerate each other. Does experience estrus (heat) every three to five days, so most does will become pregnant within one to five days of being placed with a buck. To increase the chances of pregnancy, leave bucks and does together for up to 16 days. Always separate the prospective parents on day 16 at the latest to avoid any chance of accidental delivery with the buck still in the cage.

Week One

• During the first week of a mouse's pregnancy it will be impossible to tell visually if she is pregnant. Weighing her daily on a gram scale may reveal some weight gain. The doe's nipples may become more prominent. Subtle behavior changes might be apparent, particularly if the owner knows the doe's usual habits very well.

Week Two

• In week two of a mouse's pregnancy, it may be possible to observe something of a "baby bump" in her stomach. It is possible to feel the babies inside the mouse's uterus toward the end of week two, but this is not advised. Palpation by anyone other than a veterinarian could kill a baby, potentially causing sepsis and the loss of all babies as well as the mother.
  During week two, the pregnant doe is likely to hoard food and begin to avoid contact with the buck, if they are still housed together.

Week Three

• The third week of a mouse's pregnancy is characterized by rapid weight gain. Some mice at this stage look like they've swallowed a golf ball. Others may look no different than they did before they got pregnant. The possibility of concealing a pregnancy in this way makes it critical that the buck and doe are separated by day 16 even if the doe doesn't appear pregnant.
  Mice about to deliver large litters may seem uncomfortable and restless. It's okay to hold a pregnant mouse at this time, but be gentle and allow her always to balance on all four feet on your hands or lap. Never squeeze a pregnant doe's belly.

Delivery

• Most mice give birth easily and uneventfully. The babies will squeak loudly when hungry. Do not disturb a mouse for two days after the delivery of a litter, except to fill water bottles and food bowls. As long as you continue to hear squeaking, the babies are alive and well. Complications during delivery are rare and can usually be sorted out by the mouse with time, although the babies may not survive if complications keep the mother away from her nest for a long time. If a mouse that seemed to be in labor (frantic nesting, hiding in the nesting box, small amounts of blood observed in the bedding) has not produced any babies within 12 hours, it's time to see the vet.