Twins, triplets, and other multiples (Cradle Club)

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Twins, triplets, and other multiples

If you are pregnant with more than one baby, you are far from alone. In the past two decades, the number of multiple births has climbed way up in the United States.

Information about multiples

In 2005, 133,122 twin babies and 6,208 triplet babies were born in the United States. In 1980, there were only 69,339 twin and 1,337 triplet births.

Why the increase? For one, more women are having babies after age 30. Women in their 30s are more likely than younger women to conceive more than one baby naturally. Another reason is that more women are using fertility treatments to help them conceive.

How twins are formed

Twins form in one of two ways:

diagram of a single fertilized egg spliting into two

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.

diagram of two, separate eggs are fertilized by two, separate sperm

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