There are more twins living now than ever before. Well, at least we think so. We only started recording the rate at which twins were born in the 1980s when it was about 1 in every 50 pregnancies (2%).
The rise of the twin rate
The rate at which twins were born went up to 2.5% in 1995. By 2001 it was 3%, and it rose to 3.3% in 2010.
Alexis Madrigal of The Atlantic (cited below) explained how he calculated the number of twins as of 2014: “When the CDC calculated the number through 2009, they pegged it at 865,000. Now that several years more data is available, I recalculated the number. I took the number of twins that would have been born if the 1980 twin rate had held, and subtracted it from how many twins were actually born.
The result: 1,009,337! That’s a million extra twins from 1981 through 2012, the most recent year for which data is available.”
Why so many twins?
Madrigal also reported that “A few years ago, the Centers for Disease Control researchers looked into the phenomenon.” They did so because, from an evolutionary perspective, twins are more likely to result in premature births and low birth weights – neither of which is ideal for human survival.
The reason? They can only guess, but “Older women tend to have more twins than younger women—and older women are having more of the nation’s babies. The researchers found this demographic phenomenon accounted for one-third of the increase. They attributed the rest of it to the increase in infertility treatments, specifically in-vitro fertilization and ‘ovulation stimulation medications.'”
Reproductive technology allows for multiple embryos to be implanted during IVF, and that’s common since implanting more embryos has a better chance of resulting in a successful pregnancy – of course, it also increases the chance of having twins. However, as the technology gets better, more couples are opting to have just one embryo transferred.
The “twin rate” seems to have leveled off as a result, but hasn’t reversed yet. — WTF fun facts