Did you know that the number of twin births have more than doubled since the early 1970s? Today, about one of every 35 births in the United States are twins. Even more significant is the number of triplet and higher multiple births which have increased 200 percent over the last three decades.

Why the huge jump in the number of multiple births? All About Baby, located online at www.allbaby.com, has gathered some interesting multiple facts and statistics.

The most obvious reason for the growing birth rates of twins and multiples is the use of fertility drugs and treatments. These medical interventions are most often the reason for births of four or more multiples. Recent studies from the Center for Disease Control (CDC) show that approximately 43 percent of live births resulting from assisted reproductive techniques were multiples.

But fertility drugs don't tell the whole story.

Where you live could make a difference. If you reside in Massachusetts or Connecticut, a study by the National Center for Health Statistics found that the rates for twin deliveries was as much as 25 percent higher than the overall national rate. If you want to give birth to triplets, move to Nebraska or New Jersey. Both states boast a percentage of triplets that is twice the national average. On the other hand, if you reside in tropical Hawaii your chances of having a multiple will decrease to about 30 percent below the overall U.S. rate.

The time of year and the number of daylight hours also has an impact on multiple births. More fraternal twins are conceived in July than in any other month, while January has the fewest twin conceptions.

Enhanced medical care and good nutrition may play a role in skyrocketing multiple birth rates, although experts caution that it is difficult to directly link these influences. In fact, if access to state-of-the-art medicine were a deciding factor, then why does the Yoruba tribe of Nigeria have the highest twinning incidence in the entire world?

The Nigerian people attribute it to their population's consumption of a specific type of yam. Yams? That's right, scientists have discovered that these colorful vegetables contain a high level of a substance that is similar to the hormone estrogen, which could bring on multiple ovulation.

Surprisingly, age can work in a woman's favor when it comes to conceiving twins. Older mothers traditionally have a higher chance of delivering fraternal twins, with the odds increasing to one in 27 when the mother is 35 years or older.

While identical twins have no familial connection, it is true that fraternal twins can run in the family. Female fraternal twins score an impressive one in 17 chance of giving birth to their own set of fraternal twins, probably because many carry a gene for hyperovulation, which means they release more than one egg during ovulation. And, if a woman has already given birth to fraternal twins, the chance of another set increases fourfold.

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The United States has one of the highest rates of multiples, while Japan has one of the lowest with multiple births occurring one in 120 births.

Twins are either fraternal or identical. Fraternal twins share the same womb, but come from different ovum. They are as alike as any pair of siblings. On the other hand, identical twins come from the same fertilized ovum and consequently share the same genetic makeup.

Incredible fact: According to the Guinness Book of Records, Leontina Albina, from the country of Chile, gave birth to the last of her 55 children in 1981. Her offspring included five sets of triplets (all boys).

The scientific study of twins is known as "gemellology." The word twin is probably derived from an ancient German word twine, which means 'two together.'

The average weight of a singleton newborn is 7 lbs. 6 oz., but the average weight of a triplet newborn is 3 lbs. 12 oz.

Fraternal twins are much more common than identical twins. The chances of having identical twins is about one in 285.

Identical twins exhibit almost identical brain wave patterns.

Genetic factors do not have much, if any, affect on the incidence of identical twins. Identical twins do not run in families

What a concept! There is a restaurant in New York City called "Twins." It was started by twin sisters and is staffed by 37 sets of identical twins who work the same shifts. Each evening they get 10 or more sets of twins or multiples who patron their unique restaurant.

Famous people who have parented twins:

Jane Pauley and Garry Trudeau
Ricky Nelson
Jane Seymour
Cybill Sheperd
James Stewart
Margaret Thatcher
President George W. Bush
Robert DeNiro
Michael J. Fox and Tracy Pollan
Mel Gibson
Ron Howard
Muhammad Ali
Denzel Washington

Did you know that Elvis Presley and Liberace were both twins? Their siblings died at birth.

The famed advice columnist's Ann Landers and Abigail Van Buren ("Dear Abby") are twins.

William Shakespeare was the father of boy/girl twins.