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.
Most dogs are still puppies, in mind and body, through the first two years of life. Two to four weeks: Transitional period. 1  Puppy is most influenced by his mother and littermates. 2  Eyes open, teeth begin to come in, and senses of hearing and smell develop.  Puppy begins to stand, walk a little, wag tail, and bark.