Variations of growth factors in pregnant women during labor and in newborns at delivery.

To study physiological variations in serum growth factors during peripartal period, we have measured levels of a serum growth-promoting activity (thymidine activity, TA) and radioimmunoassayable somatomedin C (Sm-C) during labor in 39 women who delivered spontaneously (group A), by caesarean section (group B) and by legal abortion (LA) (group C). TA values were higher in the group A than in the group B and C, suggesting an important effect of uterine contractions in TA generation. A major role in Sm-C production seems to be played by the length of gestation since Sm-C concentrations were significantly higher in mothers delivered by caesarean section than in LA women. During labor influence of estrogens and progesterone in growth factor production seems unlikely because of the lack of correlation with TA and Sm-C levels. The lower TA values in placental flow than in the capillary blood of newborn suggest that serum growth factors, measured as TA, are produced by the newborn and do not cross through the placenta. These data suggest that the absolute dependence of the fetus on the mother does not preclude instances of fetal autonomy.