ABSTRACT
The demographics of multiple births are well studied in the Nordic countries. Indeed, marriages, births, deaths and migrations out of and into local parishes have been recorded for centuries, in Finland for example since 1686, but wider coverage exists since 1730-40. Further information on historical as well as current record-keeping is available at www.genealogia.fi, also in English. Eriksson and collaborators extensively documented multiple birth rates from historical times up to the 1990s for Finland and Sweden1-5. Twinning rates in Finland were quite high until the late 1950s, and corresponded to general European levels in the 1960s and 1970s. In Sweden, the twinning rate declined quite dramatically from the 1920s onwards from about 12/1000 maternities to around 8/1000 maternities in the 1960s. This decline occurred even after taking into account changes in maternal age distribution. Corresponding data on Denmark and Norway have also been published. A falling trend in the twinning rate was reversed in Denmark around 1970 and, from 1970 to 1984, an increasing trend was observed6.
