Unlike dogs or cats, dwarf hamsters can be difficult to sex accurately. Due to their small size and lack of distinguishing sexual organs before maturity, it can be tough to determine if your hamster is male or female in the first few weeks. If you aren't sure if your hamster has reached maturity yet, you may try this sexing method each week until you have successfully decided whether your dwarf hamster is male or female.
Turn the hamster over so you can see its belly. You may have to hold it firmly with one hand so it doesn't flip over.
Look for nipples on the hamster's chest. There will be two rows of nipples on a female, and they are particularly hard to see on dwarf hamsters. You may use your fingers to feel for nipples on either side of the rib cage. The male dwarf hamster does not have nipples.
If you can't see or feel any nipples, examine the region around the hamster's anus. There will be two holes at the base of the dwarf hamster's belly, the lower hole being the anus and the upper hole leading to the sexual organs. In female dwarf hamsters, these two holes will be very close together, sometimes appearing only as one hole. In male dwarf hamsters, the two holes will be spaced further apart.
Other identifying features of a male dwarf hamster are the more rounded genital area (where the testicles are located) and a scent gland located mid-belly. The female dwarf hamster will have a more pointed genital area, and the sexual organs will be more inward-facing. The male dwarf hamster has smaller sexual organs than the female, and the area will not look as swollen.
You can repeat this sexing procedure at various times of day, over the course of several weeks, to be sure. Eventually, the female sexual organs will be come more noticeable or the male testicles will become more pronounced.