Högberg U, Wall S
Department of Obstetrics and Gynaecology, Umeå University, Sweden.
J Biosoc Sci. 1992 Oct;24(4):487-96. doi: 10.1017/s0021932000020046.
The change in parity and maternal age in Sweden accounts for the decline in the twinning rate from the 19th century to the middle of the 20th century. The later decline in twinning rate cannot be explained by changes in maternal age and parity. Fecundity appears to be higher in mothers of twins than in other mothers.
