In multiple pregnancies (twins, triplets and more) the metabolic rate of the mother is greater than in women who are carrying a single baby so that a high-calorie diet may also help maintain the mother's nutritional state. Multiple pregnancies have a higher risk of complications for women and their babies than do single pregnancies. In particular, poor growth of the babies in the womb, premature birth, and low birthweights are more common.
It has been suggested that a special high-calorie diet for the pregnant woman might improve the outcomes for the babies. However, boosting weight gain artificially might not bring any advantage and might be unpleasant for the mother. It might even contribute to long-term problems for her of being overweight. This Cochrane review aimed to identify quality controlled studies that compared special diets with normal diets, but found none. That is, there is no evidence from randomised trials to advise whether specific dietary advice for women multiple pregnancies does more good than harm.