FACTORS ALTERING CONCENTRATION OF CAROTENOIDS 489 



and Vitamin A. (a) Maternal-Fetal Transfer of Carotene and Vitamin A. 

 Dann 854 is of the opinion that the placenta is impervious to the carotene 

 in the maternal blood. On the other hand, Clausen and McCoord 855 

 indicated that the carotene value in the blood plasma of the umbilical vein 

 (blood flowing to the fetus) was greater than that in the umbilical arteries 

 (blood flowing from the fetus), although it is possible that the missing 

 carotene may have been retained in the fetus as vitamin A. However, the 

 more recent results of Lund and Kimble 856 and of Byrn and Eastman 857 

 are particularly illuminating in this connection. Carotene values of cord 

 blood in 149 normal infants at term were exceedingly low, averaging 23 

 ng. (range 9 to 75), as contrasted with a figure of approximately 220 ^g- in 

 the mothers (range 50 to 550). 856 Thus, the carotene ratio in the maternal 

 and fetal bloods was 10:1. In the studies of Byrn and Eastman, 857 the 

 values of carotene in fetal blood averaged only 2.01 microgram per cent, 

 as contrasted with a mean in the maternal blood of 106.3 microgram per 

 cent. This gives a ratio for carotene in maternal and in fetal blood of 50:1. 

 These data all support the fact that the placenta largely bars the entrance of 

 carotene into the fetus, with the result that the carotene level of the blood 

 of the newborn is exceedingly low. Hoch 858 reported that, whereas 0- 

 carotene represents 53 to 72% of the total carotenoids in maternal blood, 

 it accounted for only 37 and 40% of the total in two cases of newborn 

 infants. 



There is a much closer correspondence in the values of vitamin A in the 

 maternal and in the fetal bloods, respectively. According to the studies 

 of Lund and Kimble, 856 90% of the infants had plasma vitamin A values 

 between 9 and 21 microgram per cent (30 to 70 I.U.), while the values in the 

 maternal bloods ranged from 22.5 to 36 microgram per cent (75 to 120 I.U.). 

 Ordinarily, the concentration of vitamin A in the fetal blood was about 

 one-half of that in the mother's blood. The vitamin A levels in the maternal 

 blood were much more subject to change than were those in the fetal blood, 

 which remained quite constant, irrespective of whether increased or de- 

 creased values for vitamin A obtained in the mother's blood. The average 

 value for vitamin A in fetal blood, as reported by Byrn and Eastman, 857 

 was also definitely lower than that of maternal blood, but the variations 

 were not as great as those reported earlier. The average plasma vitamin A 

 level for non-pregnant women was given as 40.2 microgram per cent, while 



855 S. W. Clausen and A. B. McCoord, /. Pediat., IS, 635-650 (1938). 



859 C. J. Lund and M. S. Kimble, Am. J. Obstet. Gynecol, 46, 207-221 (1943). 



857 J. N. Byrn and N. J. Eastman, Bull. Johns Hopkins Hosp., 73, 132-137 (1943). 



888 H. Hoch, Biochem. J., 38, 304-308 (1944). 



