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Twins and Triplets

Having twin or triplets, also called multiples, is increasingly common in the U.S.

In the past 20 years, the number of multiple births has increased dramatically in the U.S.. The number of twins born has doubled and there has been a 5-fold increase in the number of triplets born. (1,337 triplets born in 1980 and 6,208 triplet babies born in 2005.)

The increase is partially due to more women having babies after the age 30. Women in their 30's are more likely than younger women to conceive more than one baby naturally. Another reason is that more women are using fertility treatments that can increase the likelihood of multiple births.

How Twins Are Formed

Twins form in one of two ways:

  1. Identical twins occur when a single fertilized egg splits into two. Identical twins look almost exactly alike and share the exact same genes. Most identical twins happen by chance.
  2. Fraternal twins occur when two, separate eggs are fertilized by two, separate sperm. Fraternal twins do not share the exact same genes — they are no more alike than they are to their siblings from different pregnancies. Fraternal twins tend to run in some families.

Multiple births can be fraternal, identical, or a combination. Multiples associated with fertility treatments are mainly fraternal.

Pregnancy with Multiples

Because of advances in prental care, including the greater use of prenatal ultrasound, most women learn about a multiple pregnancy early during the pregnancy.

If you are pregnant with twins or other multiples, you will need to see your doctor more often than women who are carrying only one baby because your risk of complications is greater.

Women carrying more than one baby are at higher risk of:

More freqent prenatal visits help your doctor to monitor your and your babies' health. Your doctor will also tell you how much weight to gain, if you need to take extra vitamins, and how much activity is safe. With close monitoring, your babies will have the best chance of being born near term and at a healthy weight.

After delivery and once your babies come home, you may feel overwhelmed and exhausted. Ask for help from your partner, family, and friends. Volunteer help and support groups for parents of multiples also can ease the transition.

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