The more babies a woman is carrying, the more likely it is that her uterus will swell, triggering contractions, says Brian Brost, M.D., associate professor of maternal/fetal medicine at the Mayo Clinic, in Rochester, Minnesota. An early due date isn't the only challenge to having multiples.
Dogs do not menstruate like humans do. Instead, they come into estrus (come into heat/season) about twice a year, once they have reached sexual maturity. This can sometimes be associated with a small amount of blood from the vulva, but it is not truly a period. Female puppies can reach sexual maturity potentially as early as six months old, although the first season (which is the closest equivalent to getting their period) is often at about nine months old.
The greatest puppy development changes happen from birth to twelve weeks of age. But from twelve weeks on, your fur-kid still has lots of growing up to do. Juvenile Period. The juvenile puppy period generally begins at age ten weeks and lasts until puberty and the onset of sexual maturity. It is during this period that puppies begin to learn the consequences of behavior and determine what is most appropriate to certain circumstances.