As a twin and the daughter of a twin, I'm really interested in twins! Above, Sis and me when we were tiny tykes with a little bit of hair. We don't know who's who in this photo, but I'm older by a matter of minutes. 👍
Twin birth rates
Sis and I recently did a deep dive into twin research. We learned that in the United States, twin births account for 30.7 of every 1,000 births (as of 2023, the latest statistics available). That means just over 3 percent of US births are twins, while a whopping 97% of US births are singletons.
Yet identical twins stand out even more: only about 4 out of every 1,000 births are identical twins. In other words, identicals represent less than half of one percent of all births, worldwide.
Identical twins are always same sex, because they are the result of one egg that spontaneously splits. In contrast, fraternal twins can be same sex or opposite sex, because they develop from two separate eggs. Here's more about the difference between identical and fraternal twins.
Key fact: fraternal twins tend to run in families, but identicals don't. By the way, the highest rate of twin births in the world is in southwest Nigeria, where 45 of every 1,000 births are twins--primarily fraternal twins.
One or two placentas?
Mom and Dad always insisted that Sis and I were fraternal twins, because there were apparently two placentas. These days, the common wisdom that identicals always share one placenta has been disproved: sometimes identical twins each have their own placenta!
DNA testing is the only scientific way to confirm whether twins are identical or fraternal, which is how Sis and I are absolutely certain that we're identical. Sis says she "always knew" we were identical, but until DNA came along, I trusted my Mom's belief that we were fraternal. I have to admit, Sis was correct all along. 👏
