The Associated Press photo looks like a gathering of a very large and popular middle school club. And in a way, it is. The 46 teens pictured are actually 23 sets of twins who recently graduated from eighth grade at Pollard Middle School in Needham, Massachusetts.
You can spot the identical twins in the photo easily, amid their more numerous fraternal twin pals.
The AP story said that the twin pairs made up about 10% of the eighth-grade class at that school — and school officials said they’d never seen anything like that number of twins.
But twin births have over the decades become increasingly common. A 2021 study in the journal Human Reproduction is facetiously called “Twin Peaks.” And the subhead notes “more twinning in humans than ever before.”
Since the 1980s, on average worldwide, twinning has increased by a third to 12 twin deliveries per 1,000 deliveries. About 1.6 million twin pairs are born each year. The researchers, who hailed from the United Kingdom and France, reported that “in recent decades, twinning rates have been increasing in the wealthier parts of our world as a result of the rise in medically assisted reproduction and delayed childbearing.”
When the researchers analyzed data from as many countries as they could find — 112 in all — they learned that in 74 of those, twinning rates increased by more than 10% between the 1980-85 and 2010-2015 time periods they compared. The biggest increases were in Europe, North America and Asia. Asia and Africa together account for about 80% of twin deliveries worldwide.
The U.S., Canada, the European Union, Israel, South Korea, Taiwan and almost all African countries have more than 15 twin deliveries per 1,000 deliveries, according to the study. Statista points out the number in 2022 in the U.S. was 31.2 twins (not pairs, but babies who are twins) per 1,000 live births.
The trend has generally been upward in America since 1980, despite some dip between 2014 and 2018, as was reported by the Centers for Disease Control and Prevention.
Older moms, those 45-54, had the highest twin birth rates in the U.S. And overall, the states with the highest twin birth rates are Alabama and Michigan.
Fraternal twin births are much more common than identical twin births.
Identical twins are not always identical, by the way. Mirror-image twins also split from the same egg to form two people, but approximately 25% of identical twins are alike in a reflection way, not a same-same way. Healthline reports that it’s believed the egg splits later in the process to form mirror-image twins. Regardless, one is left-handed, the other right. One might have a birthmark on the right side, the other the same birthmark on the left. They typically have identical skin, eye and hair colors, per the article. But hairlines, teeth, moles, dimples and other features may be like looking in a mirror.
And speaking of identical twins, some experts say the easiest way to tell them apart at the baby stage is their belly buttons, because two umbilical cords will never be tied off the exact same way. It’s foolproof.
Twins are big in mythology and literature: Think Romulus and Remus, Apollo and Artemis, Castor and Pollux, Fred and George Weasley of Hogwarts fame or even Tweedle-Dum and Tweedle-Dee.
Twin births tend to be a little more complicated, since twins usually deliver a little early, around 36 or 37 weeks, and they tend to be lower birthweight than a singleton. They are also more likely to spend a little time in the newborn intensive care unit.
Fun facts about twins
Here are 13 things we found online about twins:
- They make up a language of their own. Lomalindafertility.com’s Dr. Fihan Bareh reports that “around 40% of twins make up their own languages. Usually the special lingo disappears as their vocabulary expands.”
- It’s widely believed but not well proven that twins can read each other’s mind.
- Twins are left-handed more often than other children, at about 20%, compared to about 10% of the general population, per Bareh.
- Female twins are more common than male twins or male-female twins, according to study.com. But Psychology Today says among fraternal twins, boy-girl combinations account for about half.
- Identical twins have different fingerprints. Dr. Claire Asher told BBC Science Focus Magazine that they’re a little different for each twin because both genetic and environmental factors in the womb influence how they develop. Babies in the womb touch different things as they’re developing.
- Twins are born on average 17 minutes apart, according to Baher. And that 17 minutes can cross the date, the month or even the year on the calendar. Does that mean one was a boomer and the other Gen X?
- Taller women have twins more often than shorter ones, according to a study by an obstetrician that was published in the Journal of Reproductive Medicine. That’s likely due to the fact that shorter women have less insulin-like growth factor, he said.
- Identical twins grow less alike over time. A Live Science article says environment and experience begin to create change. For example, a study from Duke University found that “when one identical twin in his late 70s has Alzheimer’s, the other only has it about 40% of the time.”
- In 2020 and 2021, July was the month more twins were born, according to Statista.
- Women who are twins themselves are more likely to give birth to twins compared to other women, according to the American Society for Reproductive Medicine, quoted by Healthline.
- There’s a “twin-inducing diet,” according to EverydayHealth.com. And it includes plenty of dairy. Vegans, who don’t consume dairy, are far less likely to have twins.
- Moms expecting twins don’t just have twice the babies; they get twice the morning sickness, per EverydayHealth.com.
- Scarlett Johansson, Ashton Kutcher, Alanis Morissette and Gisele Bündchen all have fraternal twins.