A statistical analysis has been carried out on the frequency of twin and triplet births in Poland in the years 1949-1971.
These frequencies appear to be higher than expected on the basis of Hellin's rule, there being 1 twin birth in 87 single births and 1 triplet birth in 118 twin births.
The share of MZ vs. DZ twins having been assessed through Weinberg's method, an analysis is carried out on maternal age, parity, and urban vs. rural environment. It is concluded that the frequency of polyovulation increases with parity, whereas it becomes reduced with age on account of menopause effect already at age 40.