Fetal Malnutrition(FM) may compromise more than 130,000 pregnancies/year in the USA. Postnatal treatment of FM does not increase the reduced number of cells; antenatal treatments might, but require prenatal identification of FM. We hypothesize that metabolic changes in rapidly replicating maternal leukocytes(ML) will indicate FM. In the first 67 women of a prospectively studied series, PL Protein/DNA, pyruvate kinase(PK), glucose-6-phosphate dehydrogenase(C6PD) & energy ((ATP+½ADP/ATP+ADP+AMP)×PK/AK) increased from 24 weeks to term. Protein & RNA synthesis (3H incorp) by ML were unchanged. Of 36 single births to date, 10 had ponderal indices(PI = 100×Wt ÷ I3)<3 percentile, suggesting FM. Pregnancy changes of phosphofructokinase(PFK), ADP & energy in the ML & diet protein & calorie intakes correlated with the babies' PI. ML trends for ATP, energy, & PFK differed in mothers of FM vs normal babies. Kinetic studies of PK in FM term ML showed reduced Vmax for substrates (PEP & ADP), suggesting inhibitory or allosteric effects on the enzyme. Further, ML PK is allosterically modulated by L-alanine & fructosediphosphate. Thus, some metabolic aspects of the ML seem correlated with fetal growth & may be modulated by nutrient factors, (Supported by HD 06915)