Twin Pregnancy Twins occur in about one in 80 pregnancies. The diagnosis of twins is often made quite early in pregnancy after you have a routine ultrasound scan (like a type of radar picture): two babies are seen rather than one. A twin pregnancy is sometimes suspected if the womb feels larger than expected to the doctor or midwife who examines you. Later in pregnancy, the two separate babies may be felt during an examination, and again will be confirmed by ultrasound scan. Symptoms and common problems of a single pregnancy, such as vomiting in early pregnancy, heartburn, shortness of breath, backache, ankle swelling, piles and varicose veins, may be worse in a twin pregnancy. You are also more likely to get more serious pregnancy complications. Premature labour is a major risk, and is the main reason why babies in twin pregnancies do less well than babies in single pregnancies. There is nothing that either you or your doctor or midwife can do to reduce this risk: both bed rest and a variety of drugs have been tried and found to be ineffective. You should contact your midwife or hospital labour ward if any contractions start. High blood pressure in pregnancy is about three times more common in twin pregnancies than in single pregnancies. Bleeding in late pregnancy, due either to a low-lying or partially detached afterbirth, is also more common in twin pregnancies. Too much fluid (hydramnios) around the baby can also be a problem. This, in turn, can also lead to premature labour. Anaemia is more common, as two babies make greater demands on your supplies of iron and vitamins. How does a Twin Pregnancy occur? Twins come about in one of two ways. In one form, they can happen when two different eggs join two different sperms. Each baby then has its own cord and afterbirth (placenta). These twins may be of the same or opposite sex. They will not be identical: indeed, they will be no more alike than brothers or sisters born into the same family. This type of twin is more common if there is a family history of twins. They are also more likely to occur if you are over age 35, or if fertility drugs have been used to help you become pregnant. In the other form, twins are produced when an egg and a sperm join together, but then divide into two once they have joined. Such twins will be identical, and may share a single afterbirth. Very occasionally, twins will also share the same sac (fluid cavity).