Genetic factors and fetal growth sex constitution and birthweight in twins

Fetal growth is considered a multifactorially-influenced characteristic. Genetic factors were found to play the main role in fetal growth determination, and it is the polygenic inheritance. The paper reviews the birthweights of 360 unlike-sexed two-egg twins, born at the Clinic of Gynecology and Obstetrics, Faculty of Medicine in Beograd, from January 1, 1970 through June 30, 1984. The mean birthweight differences between the male (2954.94 +/- 704.28 g) and female (2313.19 +/- 651.32 g) fetuses, amounted to 141.75 g. The difference is highly significant (P less than 0.01); variation coefficient shows that the examined groups were homogenous (VC was below 30%). The results were discussed from the genetic point of view, and particularly from the point of view of sex constitution, with special respect to the effect of Y chromosome on fetal growth. It has been known that human somatic development, body weight, bone maturation and teeth development are influenced by variety of factors. In addition to nutritional and other factors of the external environment, genetic and humoral factors are leading. The fact that fetuses with XY male constitution are heavier at birth than female fetuses with XX constitution, made us consider the correlation between genotype-phenotype, and the mentioned characteristics. This study was aimed at finding out the role of genetic factors in fetal growth, with respect to sex constitution, particularly to chromosome effect on fetal growth in unlike-sexed two-egg twins.