The rate of appearance (Ra) of glucose in plasma and the contribution
of gluconeogenesis were quantified in normal pregnant women early (sim
ilar to 10 wk) and late (similar to 34 wk) in gestation, Their data we
re compared with those of normal nonpregnant women, Glucose Ra was mea
sured using the [U-C-13]glucose tracer dilution method, Gluconeogenesi
s was quantified by the appearance of H-2 On carbon 5 and 6 of glucose
after deuterium labeling of body water pool, Weight-specific glucose
Ra was unchanged during pregnancy (nonpregnant, 1.89+/-0.24; first tri
mester, 2.05+/-0.21; and third trimester 2.17+/-0.28 mg/kg min, mean+/
-SD), while total glucose Ra was significantly increased (early, 133.5
+/-7.2; late, 162.6+/-16.4 mg/min; P = 0.005), The fractional contribu
tion of gluconeogenesis via pyruvate measured by H-2 enrichment on C-6
of glucose (45-61%), and of total gluconeogenesis quantified from H-2
enrichment on C-5 of glucose (i.e., including glycerol [68-85%]) was
not significantly different between pregnant and nonpregnant women, In
asmuch as total glucose Ra was significantly increased, total gluconeo
genesis was also increased in pregnancy (early pregnancy, 94.7+/-15.9
mg/min; late pregnancy, 122.7+/-9.3 mg/min; P = 0.003), These data dem
onstrate the ability of the mother to adapt to the increasing fetal de
mands for glucose with advancing gestation, The mechanism for this uni
que quantitative adjustment to the fetal demands remains undefined.