The mother's belly is usually pretty similar in size to women carrying singletons until six months or so. The main problem with twins is that the uterus is designed to carry only one baby. On average, twins are born two weeks earlier than singletons, at about 37 to 38 weeks gestation. The average time of delivery for triplets, however, is about seven weeks early, at about 33 weeks gestation. We don't have a good way to prevent early labor in twin pregnancies, so it's common for women to be placed on bed rest because they are contracting, have high blood pressure or to help the babies grow.
Some doctors give steroids as a precaution and to enhance maturity in the fetus.
A single course of steroids can be very helpful, but there is no advantage to giving multiple courses of steroids, which may actually endanger the baby. Since research shows no benefit for these treatments, I don't recommend them as a routine in multiple gestations. More twin pregnancies are delivered by cesarean section than are singletons and nearly all triplets are delivered that way. Twins are usually robust babies weighing 5 to 6 or more pounds and are generally well after birth with few health complications if they are born close to term. In the absence of drugs, triplets occur in about 1 in 3,600 births.