Motherhood and Childlessness in Monozygous Twins

Part. I Early Relationships

Fifty-two pairs of female monozygous twins, discordant for motherhood and between 40 and 6o years of age, were investigated to find out whether motherhood has any long-time adverse effect on physical or mental health.

In this first part of the study the material is described and intrapair psychological differences existing before the probands' first pregnancy were focused on.

The probands were found to be much older at their first pregnancies than the primiparae of the general population. The origin of this we suppose to be the same as the origin of childlessness in the co-twins either on a biological or a psychological-social level.

In 8 pairs there was a difference in the mothers' preference for the twins during childhood. In 7 of these pairs the mothers were said to have preferred the proband. No such association between the fathers' preference and probandship was found.

Intrapair dominance bore no relation to probandship.

In respect of traits of early temperament the co-twins were more often described as serious-minded and introvert. However, probandship, temperament traits and intrapair dominance showed an intricate interrelation especially with regard to serious-mindedness.

Intrapair dominance was also associated with the co-twins' childlessness. Thus significantly more voluntarily childless co-twins were said to have been dominated by their twin partners.

The findings are discussed and it is concluded that even ideal control subjects are far from identical as far as psychological factors are concerned.