It is unlikely that you've got a pregnant hamster from the pet shop if it is very young but this is very possible if it was more than 6 weeks old and still kept with others. Since many petshops sell very young hamsters, this is not as common. The age at which hamsters mature is species-specific. Sometimes, however, you will acquire an older pet. Do make sure that she has been kept with other females if she is being kept with others.
Please don't breed your hamsters without proper know-how and plans for its pups. Your hamsters could be seriously hurt if they are put together out of estrous (breeding period of the female) and your hammy's pups will be homeless. Selling hamsters is far from lucrative in Singapore! Hamsters are abundant here and it may prove hard to find friends to take them.
You will have to take note that syrians are solitary and are not to be put together for mating for long periods of time. Instead, the mating is brief and usually supervised (yes, take note!) to make sure the pair does not start attacking each other.
Dwarf hamsters are usually kept in pairs when bred and the male has been said to help the female in child rearing and even acting as a midwife. However, this is not the case in all species and you must always watch them to ensure that the male is not disturbing the female (by trying to mate with her again) or the babies.
Many people ask me how to tell that their hamsters are pregnant but it is really very difficult to describe and for new owners, difficult to tell. I used to take a peek when my syrian hamster stood up on her hindlegs and the bulge would be very obvious.
You may not be able to tell if your hamster is pregnant in the first few days from her appearance but some owners say that she might act differently - you might notice her start to hoard bedding material and food or become more nervous or jumpy. Some hamsters don't build nests right away so this is not a good indication. In the last few days, she should be quite big and it will be quite noticeable if you've been the one handling her prior to the pregnancy and know what she usually looks like.
Try to handle her less often if you suspect a pregnancy. You should change her wood shavings and give her some table scraps in the form of cooked chicken, fish or other sources of protein (not fried). If your female is noticeably large around the abdomen, she is probably past her 11th day and will give birth within the week. The gestation of the syrian hamster is one of the shortest of all mammals - 16 days. The gestation of that of dwarfs is from 18-22 days.