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.
You'll decrease your odds of having twins/multiples if...
- You (the mother) are Hispanic or Asian. The 2001 study by the National Center for Health Statistics found that women of Hispanic origin were substantially less likely to have twins than white or black mothers. Among worldwide populations, the Asian countries of Japan and China have the lowest twinning rates, estimated at 1 in 150 and 1 in 300, respectively.
- You (the mother) are under age 25. The chance that a woman would bear twins before her 25th birthday are is less than half of what it would be after age 35.
- You live in Hawaii. In a study that examined multiple birth in the United States, this tropical paradise scored lowest, about 30% below the national average.
- You're looking for identical multiples. The rate for identical, or monozygotic, multiples is random and universal; it's the same in all populations regardless of race, heredity or other factors, and it has remained constant over time. The chances of having identical twins is about 1 in 285.
Odds of Triplets/Quadruplets/Higher Order Multiples
The statistics for higher order multiples have shown a dramatic increase in recent years. The odds of conceiving "spontaneous" triplets (i.e., without the aid of fertility enhancements) is about 1 in 8,100. Researches noted a substantial -- 400%!! -- increase in the rate of triplet births over the last twenty years.
The odds of having spontaneous quadruplets are predicted to be 1 in 729,000.
It is estimated that 60% of triplets are the result of fertility enhancing treatments; while 90% of quadruplets and 99% are due to reproductive technology.
(Note: These statistics are estimates, gathered from several sources, including a 2001 National Vital Statistics Report from the Centers for Disease Control and Prevention, Odds - Twins from BabyMed.com, Facts About Multiples: Twin Basics Page 2 web page, and Twinstuff.com.)