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.

Twins form in one of two ways:

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.

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.

Years ago, most twins came as a surprise. Now, thanks to advances in prenatal care, most women learn about a multiple pregnancy early. You might suspect you are pregnant with multiples if you have more severe body changes, including:

• Rapid weight gain in the first trimester
• Intense nausea and vomiting
• Extreme breast tenderness

Your doctor can confirm whether you are carrying more than one baby through ultrasound. 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:

• Preterm birth
• Low birth weight
• Preeclampsia
• Gestational diabetes
• Cesarean birth

More frequent 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.