Prothrombin Concentration in Newborn

Abstract

The concentration of prothrombin in the blood of babies 3 to 7 days old has been found to be essentially the same as in adult blood. 1 Curiously, however, a profound fluctuation has been observed to occur during the first 48 hours of life, as shown in Table I.

It should be noted that the prothrombin level of babies 6 hours old is relatively high and not strikingly different from cord blood. At the end of 24 hours, however, it may drop to an exceedingly low level as shown by babies 5 and 6. After 48 hours the prothrombin concentration usually has begun to return to normal. In one baby (No. 10) the return was definitely delayed since 5 1/2 days elapsed before the concentration had reached 75% of normal.

These results offer a solution to the perplexing problem of the hemorrhagic disease of the newborn. Apparently no reserve of prothrombin is built up in the fetus, and in the first 24 hours of life this clotting factor may be reduced to a distinctly hemorrhagic level. Were it not for the prompt restoration of the prothrombin, many babies would bleed. Any delay in this recovery will naturally give rise to a bleeding diathesis, and this is very probably the cause of the hemorrhagic disease of the newborn. Potentially all newborns are in jeopardy of hemorrhage, and this undoubtedly accounts for the insistence of the mosaic law that circumcision be not performed before the eighth day.

The fact that the hemorrhagic disease of the newborn responds promptly to vitamin K therapy, as Waddell, et al., 2 have reported, indicates definitely that a deficiency of this factor is the basic cause. The question remains: why the abrupt recovery? The small amount of food taken during the first 48 hours obviously can furnish little vitamin K.