Rh system and intrauterine growth. Interaction with season of birth

Based on the hypothesis that maternal-fetal genetic differences in membrane transport and signal transduction may influence intrauterine development, the recent acquisition on transport function of Rh protein prompted us to s tudy the relationship between joint maternal-fetal Rh phenotype and birth w eight. Considering that metabolic effect of maternal-fetal competition coul d be amplified by environmental conditions, we have investigated possible s easonal effects on such relationship. We have studied 5291 infants born in Sardinia in the period January 1993-De cember 1996 and 984 infants born in Rome during 1996. In Rh(-) mothers there is a significant association between season of birth and birth weight that shows the highest mean value in infants born in autu mn (i.e. conceived in winter). The association is much more evident in male than in female infants. In male infants from Rh(-) mothers, the associatio n between birth weight and season is significant in Rh(+) male newborns onl y. Recent observations by our group in NIDDM suggest that glucose transport in RBC may be related to D protein, thus we propose an interpretation of the present observation in terms of transport function. When the density of D p rotein in the infant is greater than in the mother, the balance is in favou r of the infant who may attain a significant developmental advantage when c onceived in the cold season.