The average pregnancy for twins is about 37 weeks. For triplets it is about 35 weeks. For every week the babies remain in the uterus, their birth weights increase, along with the maturity of organs and systems. Major malformations in multiple pregnancies are more common than they are in single pregnancies. The incidence of minor malformation is twice as high as it is in a single pregnancy.
Malformations are more common among identical twins than fraternal twins.
One of the main goals in dealing with multiple fetuses is to continue the pregnancy as long as possible to avoid premature delivery. This may best be accomplished by bed rest. You may not be able to carry on with regular activities during your entire pregnancy. If your doctor recommends bed rest, follow his or her advice. Weight gain is very important with a multiple pregnancy.