It turns out that the ``probability of twins being born'' is increasing all over the world, what is the reason?
A research team consisting of researchers belonging to
Twin Peaks: more twinning in humans than ever before | Human Reproduction | Oxford Academic
https://academic.oup.com/humrep/advance-article/doi/10.1093/humrep/deab029/6168658
More Twins Are Being Born Today Than Ever Before in History.
The research team collected demographic data from 165 countries from 2010 to 2015 and investigated the rate of twin births. As a result, it turned out that twins were born 12 times out of 1000 births between 2010 and 2015. Also, in a similar survey conducted from 1980 to 1985, it was recorded that twins were born 9.1 times out of 1000 births. From this, the research team claims that 'the rate of twin births is increasing.'
Below is a world map showing the ``proportion of twins born in each country'' created by the research team. Countries covered by the survey are filled in with a darker color as the rate of twin births is higher. If you check the world map, you can see that the rate of twin births is particularly high in Africa and North America.
The research team also calculated changes in the rate of twin births from the results of the 1980-1985 and 2010-2015 surveys. In the world map below, countries where the rate of twin births has increased are colored green, and countries where it has decreased are colored blue. If you check the world map, you can see that the rate of twin births has increased in many countries in North America, Europe and Oceania, and that there are several countries in South America, Africa and Asia that have decreased.
The graph below shows the number of births (blue), the number of twin births (red), and the rate of birth of twins (green) in both ``1980-1985'' and ``2010-2015'' for each region. shown in . If you check the graph, you can see that the number of births is decreasing in Europe, South America, and Asia, but the rate of twin births is increasing. Also, in North America, Oceania and Africa, both the number of births and the rate of twin births increased. Furthermore, if you check the global average, you can see that the rate of twin births is increasing.
The research team pointed out that ``the increase in the number of people using medical reproductive technology such as in vitro fertilization'' is the cause of the increase in the rate of twin births around the world. When performing in vitro fertilization, multiple embryos may be implanted to maximize the probability of success, increasing the chances of twins being born.
In addition, the research team cites 'late marriage' as another factor. Another study published in 2018 found that white women are three times more likely to have dizygotic twins when they give birth over the age of 35, and black women are four times more likely to have them.
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in Science, Posted by log1o_hf