The issue of twinning was already a concern for ancient people a few thousand years ago, but professional and modern twin researches started at the second half of the nineteenth century only. According to estimates, at least 125 million twins live worldwide nowadays. It means that, for example, the entire population of Japan would consist of twins. Moreover, annually approximately 3.9 million children are born as one member of a twin pair [1]. Other estimates are approximated from deliveries instead of the number of live births assuming 1.6 million pairs of twins were born annually in the world between 2010 and 2015 [2]. It is known from research, literature and statistical data that the rate of twin births was low in Asia and South America in the 1980s, and at a medium level in Europe and North America [1–3], but it rose in the past decades due to the increasing number of dizygotic twins. On average, every 38th child born alive is a twin. The number of dizygotic twin births are more frequent, while monozygotic twins is more rare. However, all of these show great dispersion worldwide due to different genetic endowments and sociodemographic reasons. It is indeed an exciting and special research topic, but on a social level, from a demographic point of view, it actually affects only a narrow group. In many cases, instead of answers, additional questions arise, which encourage researchers to carry out new surveys.