Your Likelihood Of Having Twins Or More

How common are twins and other multiple pregnancies?
Increasingly common, largely because more and more women are taking fertility drugs or turning to assisted reproductive technology (ART) to help them conceive. These treatments greatly increase a woman's chance of having twins or higher-order multiples. The famous McCaughey septuplets are one extreme example of the potential consequences of fertility treatments.

These days, about one in 32 births are twin births. This rate has gone up 65 percent since 1980, and it's more than double the rate among women who conceive without medical assistance — one in 89.

The rise in triplets and quadruplets is even more dramatic. Between 1980 and 1998, the rate of triplets and higher-order multiple births shot up by more than 400 percent, but it's crept back down over the past few years as fertility treatments have become more refined. In 2003, one in 535 births resulted in triplets, quadruplets, or more.

Meanwhile, the likelihood of having identical twins (when one fertilized egg divides in half) is about one in 250. This rate hasn't changed over the decades and is remarkably constant all over the world.

How likely am I to have more than one baby if I'm undergoing fertility treatment?
Fertility drugs stimulate your ovaries, increasing the odds that you'll release several eggs at the same time. On average, 20 percent of women taking gonadotropins will become pregnant with more than one baby. Women who get pregnant while taking the drug Clomid have a 5 to 12 percent chance of twins.

If you undergo in vitro fertilization (IVF), your chances of having more than one child are 20 to 40 percent, depending on how many embryos are placed in your womb. Other fertility techniques such as GIFT (gamete intrafallopian transfer) and ZIFT (zygote intrafallopian transfer) are also more likely to result in multiple pregnancies.

On its own, IUI (intrauterine insemination), in which sperm are injected into the uterus with a syringe, is the only fertility treatment that doesn't increase the chances of conceiving multiples. But most women who undergo IUI also take a fertility drug.

Fertility drugs and other treatments primarily increase your chance of having fraternal twins, where two eggs are fertilized by two different sperm. But there is now some evidence that women who undergo certain treatments also have somewhat higher rates of identical twins.

What other factors affect the chances that I'll have more than one baby?
While identical twins generally happen by sheer chance, there are several factors that influence your chances of having fraternal twins:

• Heredity: If you're a twin or if twins run in your family, you're slightly more likely to have a set yourself. Women who are fraternal twins have a one in 60 chance of bearing twins.

• Race: Twins are more common than average in African Americans and less common in Hispanics and Asians.

• Age: The older you are, the higher your chances of having fraternal twins or higher-order multiples. A 2006 study found that women over 35 produce more follicle stimulating hormone (FSH) than younger women. Ironically, increasing levels of this hormone are a sign of failing ovaries and declining fertility. But FSH is also the hormone that causes an egg to ripen in preparation for ovulation each month, and women with extra FSH may release more than one egg in a single cycle. So while older women are statistically less likely to get pregnant, if they do get pregnant, they're more likely to have twins.

• Number of pregnancies: The more pregnancies you've had, the greater your chances of having twins.

• History of twins: Once you have a set of fraternal twins, you're twice as likely to have another set in future pregnancies.

• Body type: Twins are more common in large and tall women than in small women.

source from http://www.babycenter.com