These days more twins are being born than ever, according to a study by the University of Oxford.
Researchers say the trend can be attributed primarily to increased fertility treatments and parents forming their families later in life.
The new study, published in the academic journal Human reproduction, shows that the global twin birth rate has risen by a third since the 1980s, from just over 9 twin births per 1,000 deliveries to 12 per 1,000. That equates to 1.6 million pairs of twins every year.
Asia and Africa currently account for 80 percent of all twin births in the world, but Europe, North America and Oceania are catching up fast, according to the analysis.
The researchers analyzed twinning rates between 2010 and 2015 in 165 countries covering 99 percent of the world’s population. For 112 countries, they compared it to twinning rates from 1980-85.
They found that twinning rates had more than doubled in Europe over the past 30 years, and had even skyrocketed by 71% in North America.
There are two reasons behind the trend, Gilles Pison, a researcher at the French Institute for Demographic Studies, told Euronews.
“First, the development of medically assisted reproduction is associated with a higher frequency of twin births. This development has mainly taken place in developed countries,” he said.
“Second, the fact that women are having their babies later and later in many countries around the world, especially in the most advanced countries. In fact, the risk of twin pregnancies increases as women age.”
But twinning rates may now have reached a peak. With twin pregnancies at higher risk for complications, premature delivery, and low birth weight, health regulators are increasingly recommending fertility clinics to refine their techniques to support singleton pregnancies.
“When IVF treatment took off 30 years ago, medical teams implanted multiple embryos at the same time into the woman’s body to increase her chances of success,” Pison explained. “This was considered a problem because multiple pregnancies are not easy. Twins or triplets are fragile children.”
“Now they are trying to implant one embryo at a time. If the first attempt fails, they can quickly re-implant an additional embryo that has been frozen in the meantime.”
The odds of a woman having twins also seem to peak around age 37. That’s because the level of follicle-stimulating hormone (FSH) in the blood increases as women age.
“This hormone helps the eggs in the ovaries grow and mature, and it also plays a role in ovulation. When its level increases, so does the double ovulation rate within a woman’s menstrual cycle,” Pison explained.
“Beyond 37 years, the twin rate decreases. This is due to the higher mortality rates for early-stage embryos, as well as dysfunctions in ovarian activity. Therefore, although the level of the FSH hormone continues to rise, higher embryonic mortality means twinning rates start to fall. “
George is Digismak’s reported cum editor with 13 years of experience in Journalism