Renal function before birth

Abstract

Urine has been collected from infants at the moment of birth and compared in composition with the first urine formed after birth, and with the maternal urine. Cord serum and maternal serum have also been analyzed. Cord serum differs from maternal serum in that it contains a higher concentration of P and frequently also of K. Foetal urine differs from maternal urine formed at the same time, and from the urine formed by an infant immediately after birth in that: (a) It usually has a very low osmolar concentration (average 137 mosmol./l.). The fraction of the osmolar concentration due to NaCl is large and of that due to urea correspondingly small. (b) It usually contains slightly more Na than Cl. (c) It contains little K and only the merest traces of inorganic P. It follows that sodium chloride in excess of requirement must continually be entering the foetus and that free water must also in some way be made available. The character of the urines can be explained if the kidney before birth is outside the control of the anti-diuretic hormone, the parathyroid hormone, and possibly the suprarenal hormone.