Nitrogen balance studies in human pregnancy.

Sixty-eight primigravidae successfully complete a 12-day nitrogen balance study when they were between 30 and 34 weeks pregnant. Particular attention was paid to ensure that each patient ate a hospital diet quantitatively equal to the home diet; each patient ate the same every day and all food was eaten. There was a significant correlation between nitrogen intake and apparent nitrogen retention but no relationship between apparent nitrogen retention and birth weight or the occurrence of pre-eclampsia. The mean apparent nitrogen retention for the 68 women was 1.2 g/day. Once allowance is made for integumental losses this figure is equal to the estimated daily nitrogen retention for growth of the fetus and reproductive tissues during this time. There was no evidence of maternal storage of surplus protein as has been previously suggested. The previous literature is reviewed and an attempt made to explain the discrepancy between the findings in this study and previous work.