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.
Half of male dogs will display mounting behavior by 5Â½ months of age, and will become able to sire a litter around that age. Note that some male dogs may be able to sire a litter before 5 months of age - 5 months is the average. Female dogs become sexually mature (have their first heat) between 5 and 12 months of age.Small breed dogs tend to have their first heat around 5-6 months, while some giant breed dogs will not start to cycle until they are 18-24 months of age.. Male puppies will display mounting behavior at a very young age (3-4 weeks), but are not producing sperm. This puppy mounting behavior will often disappear in a short time and then reappear as the dog approaches puberty.