Since the 1980s, double births have increased from 9 to 12 per 1,000 deliveries
Africa is the region with the highest birth rate for identical twins and twins Getty Images
Twin births hit a global high
Never have so many twins and twins been born as in recent years. A study published this week in the journal Human Reproduction shows that since the 1980s, the rate of joint births has increased from 9 to 12 per 1,000 deliveries, which means that one in 42 children born in the world is a twin.
The study finds that one of the main causes of this increase is the increase in assisted reproduction, as well as the delay in maternity observed in many countries during the last decades.
The research compared the delivery rates of monozygotic (identical twins) and dizygotic (twins) twins from 1980 to 1985 with that from 2010 to 2015. It included information from 112 countries for the early years and from 165 countries for the more current . These were obtained from statistical offices, demographic research institutes, individual survey data, and medical literature.
The results show that twin rates have reached an all-time high. “We could be at a peak in an absolute sense,” say study authors Christiaan Monden, from the University of Oxford (England); Gilles Pison, from the Natural History Museum in Paris (France); and Jeroen Smits from Radboud University (The Netherlands).
Except for the poorest countries in Africa and South Asia, as well as several countries in Central and South America, most nations showed a substantial increase in double births, proportions that in some cases reached more than 70 %.
The largest increases were seen in Europe, North America and East Asia. Greece, Denmark or South Korea are some of the countries where the phenomenon has increased the most.
Twins of Asian origin
Africa and Asia Asia account for 80% of all double births in the world. Flickr RM
Africa, which did not show a significant increase between the two periods, continues to be the continent with the highest rate of twins. Together with Asia, both areas currently host 80% of all double births in the world.
South America is the only region where fewer twins and twins are being born now. The most likely explanation for the authors is the decrease in deliveries in general, since the proportion of twins in births has not changed much.
That the richest areas of the world and emerging economies are those that show the greatest increases is no coincidence. The changes have been largely driven by assisted reproduction – which includes in vitro fertilization, ovarian stimulation and artificial insemination – and late motherhood, both of which increase the likelihood of multiple births.
Source of complications
In vitro fertilization techniques began to be regulated by the increase in twin births
The sharp increase in the number of twin births due to medical interventions in reproduction and fertility began to generate concern in the 1990s. Twins, especially monozygotic twins, present more complications during pregnancy, birth and after both, including premature births, low birth weight, or increased infant and maternal mortality.
So IVF techniques began to be regulated. “The trend was clearly marked by the Scandinavian countries, but we all follow it. Who else and who has been reducing the number of embryos implanted in women to try to avoid multiple births ”, explains the biologist specialized in assisted reproduction Anna Veiga, from the Catalan clinic Dexeus Mujer.
In Spain, one of the leading countries in assisted reproduction, this change began to occur about 10 years ago, according to Veiga. This means that the study data does not exactly reflect the current situation, but it does offer a global picture and of the patterns of the different regions.
For example, some countries such as Denmark or Finland have reached a maximum peak and a subsequent decline in the birth of twins. The study did not find such a ceiling in our country, but it is likely that the regulations on in vitro fertilization have already marked this trend as well.
The authors plan to develop another study that e span through 2020 to more closely approximate the current situation and better reflect changes in twin and twin rates.