Hamsters grow up fast and can start to reproduce when they are less than 2 months old. Learning to sex your baby hamsters is important so you can separate the males from the females and avoid unwanted pregnancies -- and even fights.
Testicles in the male may not be evident until the hamster is 4 weeks old. If you want to determine the sex of your hamster before he's a month old, you might need to look at other clues. One simple difference is that the teats are clearly visible in females by the time they reach 8 days of age. Look at the distance between the anus and the genital opening. The distance between the two is smaller in females. This might be difficult to gauge if you only have one baby hamster, but if you can compare several babies of similar age, you can differentiate the males from the females this way.
If you're conducting a physical examination, a few other clues can help you sex a hamster. For example, females have a more pointed posterior, while a male's posterior is more rounded. In some types of hamsters, such as dwarf hamsters, you can clearly see a scent gland near the anus in males, while the glands are flatter and harder to see in other species.
By the time your hamster is 4 weeks old, you should start noticing the testicles on males. Some types of hamsters, like the Campbells Russian Dwarf and the Winter White Russian Dwarf, might be more difficult to sex because they are very small and the testicles might not be as apparent at first. Still, you should be able to see a small swelling around the anal area that indicates the presence of testicles.
Holding the Babies Properly
To make sex identification easier and to prevent the hamsters from slipping from your hands and falling, turn the hamster onto his back on the palm of your hand and use your fingers to hold his neck and his stomach down. This way your other hand is free to check the genital area and brush hair away if needed to see more clearly.