What Are the Odds of Having Twins?

About the Odds of Having Twins

Among general populations, the chances of having twins in the 21st century are about 3 in 100, or about 3%. Your chances are better than ever; researchers have recorded an increase of nearly 60% since the early 1980s. The most recent statistics, part of a 2006 study by the National Center for Health Statistics show that twins represented 32.21 of every 1,000 births.

Increasing the Odds of Having Twins

You'll increase your odds of having twins/multiples if:

•You (the mother) are over age 45. The chances of having twins increases with age; 17% of mothers over the age of 45 give birth to twins. Becoming a mother after age 50 boosts your odds considerably, to nearly 1 in 9!

•You live in Massachusetts or Connecticut. A 1999 study found that rates in these states were at least 25% higher than the national rate in the United States.

•You take fertility drugs or undergo other fertility treatments. No one can deny that the availability of fertility enhancements has increased the multiple birth rate, but no study seems to conclusively pinpoint the impact. Some estimate that the chances of having twins after fertility enhancing treatment is as high as 1 in 38. Others estimate that using the drug Clomid increases your chances to 1 in 5.

•You, your mother, or her mother's mother is a fraternal twin. These women may carry a gene for hyperovulation, which means they release more than one egg during an ovulation cycle increasing their ability to conceive fraternal twins. The chances may be high as 1 in 17 if the mother is a fraternal twin herself.

•You've already had one set of fraternal twins. For mothers who have already had one set of fraternal twins, their chances of conceiving another set are four times greater than the average woman, or about 1 in 12!

•You're Nigerian. This African country purportedly has the highest twinning rate in the world, estimated at 1 in 22. Some sources attribute it to their consumption of large quantities of yams. It's worth a try if you really want to have multiples!

•You're overweight or tall. A study published by the American College of Obstetrics and Gynecology reported a significant increase in fraternal twin births to mothers who had a BMI of 30 or higher, or who were in the top 25th percentile for height.