[Role of paratypical factors in determining human multiple pregnancy. I. A comparative statistical analysis of the social biology characteristics of the mothers].

Twelve social-biological characteristics were investigated in 400 mothers of monodizygotic twins and in 429 women in the control group. The mean age of mothers for dizygotic types of twins was, on the whole, authentically higher than that of the control women. The continuance of the working activity, the character of the work, inclination towards certain food have been reported to influence the manifestation of being a dizygotic twin. In addition to the above mentioned factors, the age of women at the beginning of their sexual life is of importance. Also, a woman's psychological attitude towards the possible pregnancy is reported to influence multiple pregnancy. The percentage of repeated marriages among twins mothers was higher than that in the control group. Conclusions are made on the use of the factors investigated for a probable estimation of manifestation of multiple pregnancy.