Female chins have two uterine horns, which is essentially like having two uteruses. Thus she can become pregnant in each uterine horn, at separate times. Some people believe this is why you sometimes have a litter where one kit will weigh 50 grams and another will be 20 grams. But more commonly, the female will either pass the kits underdeveloped and they will not survive, or they will be reabsorbed by the uterus.