What are your odds of having twins?

Do twins run in your family? If you're pregnant with twins, you can count on hearing that question a lot over the next several months. . .and after their birth, for many years to come.

What are the odds of becoming pregnant and having twins? Several factors can affect your chances. Let's take a look at the most common ones (and provide you with some ammunition to answer that ever-present, sometimes annoying question):

Use of fertility treatments - The steady rise in twin (and multiple) pregnancies in recent years is due in large part to the increased use of fertility drugs and in vitro fertilization (IVF).

Fertility drugs stimulate your ovaries so your chances of releasing several eggs at once is greater. For example, women taking the fertility drug Clomid have a 5 to 12 percent chance of having twins.

The use of in vitro fertilization (IVF) increases your chances of having twins or more by 20 to 40 percent, depending on the number of embryos placed in your womb.

The use of fertility treatments generally increases your chance of having fraternal twins or more, where two or more eggs are fertilized by two or more sperm.

Heredity - You may have a greater chance of having fraternal twins due to hereditary factors. (Hence, the question, "Do twins run in your family?) Mothers can pass on the tendency for hyper-ovulation (or releasing more than one egg in a reproductive cycle) to their daughters. The chances are greatest for:

  • Women who have already given birth to fraternal twins
  • Women with a history of fraternal twins on the mother's side of the family.
  • Women who are fraternal twins.

Age - As women age, they release higher levels of hormones, which encourages the release of more eggs from their ovaries. Along with the fact that more women are waiting longer to start their families, we have seen a higher incidence of twin pregnancies in older women.

The incidence of twins peaks at about the ages of 35 to 39 for white women in the United States. African-American women in the United States actually see an increased incidence though the age of 49. Although there is a general decrease in twin births between the ages of 40 and 44, the incidence of supertwins in this age group has increased significantly in recent years.

Race - Statistics show that twins are more common in African-American women than in Caucasian women. They are less common in Hispanic and Asian women overall.

Number of pregnancies - Your odds of having twins increase the more times you become pregnant.

Body type - Twins are generally more common in women who are taller and larger than in small women.

While some of the studies done about the odds of having twins have been conflicting, the factors listed above are the most common possible reasons cited for having twins. Of course, some women have one or more of the factors listed above and never have twins. Other women have none of these factors and, from seemingly pure luck, become pregnant with twins or more.

So, while some women believe they can "do something" to increase their odds of becoming pregnant with twins, it's not that simple. But, as any mom of twins or more can attest, if you are lucky enough to experience a twin or multiple pregnancy, it's truly a special gift when your babies are born.

Are you having twins? Review our list of twin pregnancy symptoms.

Confirming it's twins - twin ultrasounds. . .

Video: 4-D Twin Ultrasound

Your Feelings: Finding Out It's Twins