Would you be surprised to learn that you're carrying twins or even triplets?

Sometimes a twin pregnancy just happens. In other cases, specific factors are at play. For example, a twin pregnancy is more likely as you get older because hormonal changes may cause more than one egg to be released at a time. Use of assisted reproductive technologies — such as in vitro fertilization — also boosts the odds of twins or other multiples.

If you're diagnosed with a twin pregnancy or other multiples, here's what you need to know to take good care of yourself — and your babies.

Fraternal twins — the most common kind — occur when two separate eggs are fertilized by two different sperm. Each twin has his or her own placenta and amniotic sac. The twins can be two girls, two boys, or a boy and a girl. Genetically, they're no more alike than any other siblings.

Identical twins occur when a single fertilized egg splits and develops into two fetuses. Identical twins may share a placenta, but each baby usually has a separate amniotic sac. Genetically, the two babies are identical. They'll be the same sex and look exactly alike. Rarely, identical twins fail to completely separate into two individuals. These babies are known as conjoined twins.

Triplets and other higher order multiples can be identical, fraternal or a combination of both.

Your health care provider may suspect a twin pregnancy if your uterus is larger than normal or there seems to be more than one fetal heartbeat. Certain blood tests may suggest twins or other multiples as well. A suspected twin pregnancy is typically confirmed with an ultrasound. During this exam, sound waves are used to create images of your uterus and baby — or babies.

Sometimes a seemingly normal twin pregnancy is later found to have only one baby. This is known as vanishing twin syndrome. Such an episode can be heartbreaking, frustrating and confusing. Often, there's no clear explanation for the loss.

Taking good care of yourself is the best way to take care of your babies. During a twin pregnancy, you can expect:

• More frequent checkups. You'll see your health care provider often to track your babies' growth and development, monitor your health, and watch for signs of preterm labor. You may need frequent ultrasounds or other tests. Your health care provider may recommend every-other-week visits during the second trimester and once-a-week visits during the third trimester.
• More emphasis on certain nutrients. You'll need more folic acid, calcium, iron, protein and other essential nutrients. If you're already eating healthfully, keep it up — and be sure to take a daily prenatal vitamin. Your health care provider may recommend an iron supplement as well.
• More weight gain. Gaining the right amount of weight can support your babies' health. It also makes it easier to shed the extra pounds after delivery. For twins, the recommendation is often 35 to 45 pounds (about 16 to 20 kilograms) for women who have a healthy weight before pregnancy — which may require about 2,700 calories a day. Work with your health care provider to determine what's right for you.
• More precautions. Your health care provider may ask you to limit some of your activities — such as work, travel and exercise — as your pregnancy progresses. Although bed rest hasn't been proved an effective way to prevent preterm labor, it's sometimes suggested when there are blood pressure problems or concerns about the babies' growth.

Healthy multiples are born every day, but it's important to be aware of possible complications. For example:

• High blood pressure. Mothers of multiples are more likely to develop high blood pressure during pregnancy. When high blood pressure is combined with protein in the urine, the condition is known as preeclampsia. Careful management is needed to prevent serious complications for both mother and baby.
• Preterm birth. The more babies you're carrying, the less likely you are to carry your pregnancy to term. If you have signs of preterm labor, you may be given injections of a steroid medication to speed your babies' lung development. Even then, however, the smallest preemies may fight to survive. Complications may include low birth weight, breathing and digestive difficulties, underdeveloped organs, learning disabilities, and developmental problems. Rarely, one baby is delivered prematurely but the other baby or babies are able to continue developing in the womb. This is known as a delayed-interval delivery.
• Twin-twin transfusion. With identical twins, it's possible for a blood vessel in the placenta to connect the babies' circulatory systems. This causes one baby to receive too much blood and the other too little. This is a serious complication for both babies that may require aggressive intervention during pregnancy. Often, babies in this situation are delivered as soon as the benefits of early birth outweigh the potential problems of prematurity.
• C-section delivery. It's possible to deliver multiples vaginally. C-section deliveries are common for twin pregnancies, however — especially if the babies aren't in a head-down position. In some cases, complications after the vaginal delivery of the first twin may require a C-section delivery for the second twin. C-sections are usually considered the safest option for triplets and higher order multiples.

Healthy multiples have the same needs as other newborns. Yet with twins, you'll have a double dose. You may need more rest and support than you imagined. Take time to enjoy your babies — and ask friends, loved ones and others for help when you need it.