Pregnancy in which more than one baby is present. Twins occur in about one of eighty pregnancies. Triplets or a larger number of foetuses are extremely rare, and occur almost exclusively after treat- ment to stimulate ovulation. The chance of complications is somewhat higher in multiple pregnancy. The placentas, which are too small in proportion to the size of the babies, can sometimes be insufficient for the baby’s needs at an early stage. Malfunction of the placenta is increased by the regular incidence of high blood pressure and the increased tendency to retain fluid. These last-mentioned factors roughly quadruple the likelihood of pre-eclamp-sia. For these reasons, rest and a salt-free diet are usually prescribed from early on in pregnancy. A pregnancy in which there are twins normally lasts for less than 37 weeks and birth is premature. One complication of labour is that one of the babies is often a breech delivery. This, in the case of prematurely born, immature babies, is an additional strain which threatens survival. A woman with a multiple pregnancy is usually kept under observation; delivery almost always takes place in hospital.