False pregnancy occurs 60-80 days after the bitch was in heat, about the time a pregnant bitch would give birth. (Pregnancy in a dog lasts about 63 days.) A dog experiencing a false pregnancy may have some abdominal swelling and/or engorgement of the mammary glands which can be painful. In some cases the bitch will actually produce milk, make a nest, and even collect socks or toys and hold them against her breasts. Bitches undergoing false heats generally do not experience serious long-term problems since the behavior disappears when the circulating hormones return to their appropriate levels. However, some bitches may have a false pregnancy with each heat.
One of the advantages of spaying your dog is that you can eliminate the possibility of this condition occurring.