EFFECT OF DISPARITIES IN BIRTH-WEIGHT ON DIFFERENCES IN POSTNATAL-GROWTH OF MONOZYGOTIC AND DIZYGOTIC TWINS

Influence of intrapair differences in birth weight (IDBW) on the patte rns of postnatal growth of MZ and DZ twins from middle/late childhood to adolescence were studied in 49 MZ, 40 DZ male and 40 MZ, 35 DZ fema le pairs coming From the Wroclaw Longitudinal Twins Study. Intrapair d ifferences in the patterns in postnatal growth were expressed in sever al indices: average differences in standardized values (AST Height, AS D Weight); absolute average differences in standardized values (ABSD H eight, ABSD Weight), average Euclidean distances coefficient (EUCD Hei ght, EUCD Weight); coefficient of shape differences (SHC Height, SHC W eight); measure of deviation (MD Height, MD Weight) and correlation co efficient for the standardized attained values (CORC Height, CORC Weig ht). Relationships between IDBW and indices were based on the means of Spearman Rank Order Correlation. Additionally for 40 MZ, 35 DZ male a nd 25 MZ, 18 DZ Female pairs, the relationships between IDBW and intra pair differences in biological parameters derived from Preece Baines m odel 1, describing differences in time (DT1), height (DH1), velocity ( DV1) at the beginning of the adolescent growth spurt, differences in t ime (DT2), height (DH2), velocity (DV2) at peak height velocity and di fferences in adult height (DAH) were examined. The results showed that only in MZ girls did dissimilarity in birth weights significantly imp air the subsequent growth in stature. Furthermore, the results reveale d that birth weight influences the parameter describing adult stature in MZ girls. It is concluded that the lack of relationship in DZ twins is due to their unique genotype, which strongly determines the postna tal growth. Three possible interpretations are given as explanations o f the results obtained in this study: male excess neonates mortality, 'third factor' and programmed of growth in utero.