There have never been as many twin births in the world as there are today

The increase in the number of twin births and the background to the phenomenon were reported in the scientific journal NewScientist. Researchers at Oxford University examined birth data from 165 countries. Based on their results, between 1980 and 2015, the proportion of twin births increased by a third globally. Previously, there were 9 out of a thousand births, and now there are 12.

Much of the growth is given by bivalve twins, which develop from different eggs and sperm. The proportion of identical twins did not change during the observed period.

According to researchers, the proliferation of artificial insemination methods in high- and middle-income countries is causing the process. Treatments stimulate the ovulation of women with hormones, which often results in two eggs maturing at the same time, giving them a better chance of giving birth to twins.

The proliferation of in vitro methods also increases the rate of twin births. This is when fertilization takes place outside the body, this is often called simply a flask baby procedure. At one implant, two to three or even more embryos can be implanted in the uterus of the mothers at the same time to increase the chances of at least one fetus surviving the procedure. This process often results in the development of twin pregnancies.

Because such pregnancies are more likely to cause various complications, either preterm birth or low birth weight, new countries already require only one embryo to be implanted in the mother during the procedure. As a result of the new regulations, the number of twin pregnancies may start to decrease in the future.

However, it is not only artificial insemination that is behind the increase in the proportion of twins. It also plays a role in the fact that women in developed countries are having children later and later - and older women are demonstrably more likely to have two eggs at the same time.

Interestingly, Africa traditionally has a higher proportion of bivalve twins at birth. Scientists think there may be unknown genetic reasons for this.

If we look at the Hungarian data, we also see that the proportion of twin births has increased significantly, especially since the mid-1990s. Its latest publication on twin births was published by the Central Statistical Office in 2014, which shows that by the 1990s the proportion of twin births in Hungary was around 12 per thousand. From then on, however, it grew rapidly, reaching 20 per thousand by the 2010s.

Thus, the rate of twin births in Hungary is almost twice the world average.

This also confirms that the global phenomenon is mostly due to the prevalence of artificial insemination methods in more developed countries.

Finally, an interesting fact, triple and plural twin births are described statistically by the Hellin rule discovered in the 19th century. It has been observed that if n double births occur for every n births, a triple ^{birth occurs for every n 2} pregnancies and a quadruple birth for every n ^{3 births.} In practice, this means that if there is currently one twin birth in every 60th birth in Hungary, then every 60 ² , ie 3600 births, there is one triple birth, and every 60 ³ , ie 216 thousand births, there is one quadruple. The rule is also confirmed by practice, an average of 50 triplets are born in Hungary every year, and a total of 10 triplets were born in Hungary between 2000 and 2019.

(Source: marmalade.co.hu; hirado.hu | Image: pixabay.com)