Twins and socioeconomic factors: changes in the last 20 years.

Background: Socioeconomic factors associated with twins/multiples have been sparsely studied.
Methods: Data, regarding twin out of total births from 1996 to 2015, were extracted from databases of the Hellenic Statistical Authority and analyzed.
Results: Twinning rate in Greece has increased from 1996 and onwards, in parallel with advanced maternal age and decline in total births. Higher twin rates are associated with higher maternal education, better paid parental occupations, and thus wealthier families, married maternal status, while immigrants present a lower twinning rate than Greeks. Lastly, the years of the economic crisis, starting in the year 2008 and still continuing, are characterized by a higher percentage of twins.
Conclusions: Our findings should be mainly attributed to the postponement of fertility, as well as the treatment of infertility with transfer of multiple embryos, when assisted reproductive technologies are applied.