T. Forrester et al., UREA PRODUCTION AND SALVAGE DURING PREGNANCY IN NORMAL JAMAICAN WOMEN, The American journal of clinical nutrition, 60(3), 1994, pp. 341-346
The pattern of aggregate nitrogen demand during pregnancy and the feta
l and maternal components are unclear. Excess demand enhances efficien
cy of nitrogen utilization. Urea salvage contributes to enhanced effic
iency. Dietary protein intake, urea production, and salvage of urea ni
trogen were measured in eight nonpregnant control subjects, and trimes
terly in nine pregnant women. Production was measured after prime-inte
rmittent intravenous doses of [N-15 N-15]-urea by dilution of label in
urinary urea. Dietary protein intake was greater in trimester 1 than
in nonpregnant women (167 +/- 36 vs 224 +/- 60 mg N.kg(-1).d(-1)), and
increased further in trimester 2 (266 +/- 59 mg N.kg(-1).d(-1)). Urea
production was not higher during pregnancy. Despite higher protein in
take, urea salvage was higher in pregnancy (40 +/- 24 nonpregnant vs 7
7 +/- 23, 61 +/- 31, and 51 +/- 12 mg N.kg(-1).d(-1)). Therefore, the
demand-supply gap for nitrogen was greatest early in pregnancy when fe
toplacental growth is slowest, and implies heightened maternal demand.