10 Things You Never Knew About Twins

Twins are everywhere these days—one in every 30 babies born in 2009 was a twin (a 76 percent hike since 1980)—and you can’t flip through a gossip magazine without seeing some celebs' twins gallivanting through Central Park. You love their matching outfits and go gaga for their babbling YouTube videos, but did you know that identical twins have different fingerprints? Or that taller women are more likely to end up with a twin than shorter ladies? Read on for more wacky twin facts.

One study found that dairy lovers are five times more likely to have fraternal twins than prospective moms who shun milk and yogurt. The reason? A protein called insulin-like growth factor (IGF) increases the sensitivity of the ovaries to follicle stimulating hormone, thereby increasing the odds of simultaneously ovulating more than one egg. “Milk contains IGF, and even just a 10 percent increase in dairy consumption can influence your chance of having twins,” explains Dr. Gary Steinman, an ob-gyn at North Shore-Long Island Jewish Health System in New Hyde Park, N.Y. Also, vegans’ IGF blood concentrations are about 13 percent lower than that of women who consume dairy.

Writer Melanie Thernstrom coined the term in a January 2011 New York Times story that chronicled her own infertility journey. Thernstrom and her husband had found an egg donor and implanted two embryos in two separate uteruses—one in one surrogate, one in another. Both implantations took, resulting in “twibling” babies—twins incubated in separate bellies. “Our children were born five days apart — a fact that cannot be easily explained," Thernstrom wrote.

"When people press me about their status (‘But are they really twins?’), the answer gets long. The word ‘twins’ usually refers to siblings who shared a womb. But to call them just ‘siblings’ instead of ‘twins’ also raises questions because full genetic siblings are ordinarily at least nine months apart. … If the person continues to quibble about whether they really qualify as twins … I announce airily that they are ‘twiblings.’”

Photo via Melanie Thernstrom

Identical twins can be raised separately from one another and still wind up being very similar in personality and interests. That’s what the Minnesota Center for Twin and Family Research at the University of Minnesota concluded after studying the “Jim twins.” These boys were separately adopted at less than a month old, and both of the adopting couples chose to name their son James (unbeknownst to the other.)

When James and James reunited in 1979 at age 39, they discovered: they had both married women named Betty; one had named his first son James Alan and the other had named his first son James Allan; they both had a dog named Toy; each had received law-enforcement training and served as a part-time deputy sheriff in Ohio; math and spelling were challenges for both; at 18, both twins had begun experiencing tension headaches; and both were 6'0" tall and weighed 180 pounds.

Photo via Blog

Eryn Levis, a Skokie, Ill., mom of three, loves peeking in on her identical daughters Maya and Lauren to find them holding hands while sleeping.

“I think, because they were literally in the same ‘living space’ in my uterus, tumbling around with one another, touching one another as they developed, my twins appear to be more physically connected than other siblings,” she explains. “They also tend to lie on the couch and watch television with their arms or legs intertwined. It’s like they have separate limbs of a single being!”

Eighty-eight million views can’t be wrong. That’s how many people have tuned in to watch these chatty twin brothers babble away, speaking a language foreign to everyone but themselves. According to an Institute of General Linguistics study, 40 percent of twins invent their own languages. But one emerging theory behind cryptophasia (aka twinspeak) is that twins who continue relying on their made-up language past the early toddler years may be at risk for developmental delays. If there are mistakes in one child’s phonetics, for instance, the other one isn’t going to correct him because he somehow understands precisely what he is hearing, Le-Bucklin explains.

If you’re concerned about your kids’ twin talk, speak with your pediatrician and be sure to spend plenty of individual time with each child, talking and reading with them. “The more adult language they hear,” Le-Bucklin says, “the better their language development.”

Photo via YouTube

Could Rebecca Romijn’s mile-long (she's 5'11") legs be behind her adorable twin daughters Charlie and Dolly? More research by Steinman suggests that taller women are more likely to net a 2-for-1 pregnancy, again due to IGF. When he compared the heights of 129 women who gave birth to twins or triplets against the national average, he discovered that multiple-birth mothers averaged more than an inch taller, at 5'5" (versus the U.S. average for adult females of 5'3¾"). Taller ladies have greater levels of IGF circulating in their bodies, which could cause them to drop more than one egg at a time.

Throughout her pregnancy, Lori Foster of Austinburg, Pa., was repeatedly guaranteed by her gynecologist and the ultrasound technician that her boys were absolutely, positively, no-doubt-about-it fraternal. “Despite the fact that their measurements were the same throughout the pregnancy, he insisted they could not be identical because the placentas were so far apart,” she recalls (identical twins often share a placenta). Ultimately, they were found to be identical.

A recent University College London study found that Foster and her family are far from alone. Researchers estimate that 15 percent of parents are mistakenly told that their identical twins are fraternal. That’s because in almost one-third of identical twin cases, the zygote splits within two days of fertilization, resulting in separate placentas. (Most people automatically associate separate placentas with fraternal twins.)

So much for the perfect crime. A burglar with a twin might think he can frame his better half and get away with it, but in fact, identical twins share everything except the same fingerprints. “Fingerprint development is influenced by environmental factors like position in the womb, touching the amniotic sac and more,” explains Dr. Khanh-Van Le-Bucklin, a pediatrician at University of California-Irvine and author of "Twins 101: 50 Must-Have Tips for Pregnancy through Early Childhood From Doctor M.O.M."

Mom who are breast-feeding when they become pregnant again are a whopping nine times more likely to conceive twins than those who have stopped nursing, according to research by Dr. Steinman. That’s because a woman’s IGF levels remain elevated in order to help her produce milk, potentially increasing her odds of dropping a second egg during ovulation. Even if you’ve weaned your child, if you nursed her for 20 months, your chances of fraternal twins the next time around remains elevated.

For years, C-section has been the go-to delivery method for twins. But a New England Journal of Medicine study suggests that vaginal birth may be just as safe. “As long as first twin is head-down and your OB is good at delivering breech babies, it is recommended that a woman has a trial of vaginal birth,” Le-Bucklin says. (Most physicians still recommend a C-section if baby No. 1 is feet-first.) Benefits of vaginal delivery include less pain, reduced recovery time, faster establishment of breastfeeding and more, all of which will come in handy, since “you really have to hit the ground running with twins,” Le-Bucklin (who delivered her girls vaginally) notes.