The Use of Amniotic Fluid 3-Methyl Histidine to Creatinine Molar Ratio for the Diagnosis of Intrauterine Growth Retardation

To determine if the amniotic fluid 3-methyl histidine to creatinine molar ratio (3MH:CR) could prove useful for the antepartum detection of intrauterine growth retardation (IUGR), the 3MH:CR was determined retrospectively in 3 groups of human amniotic fluids. Group A consisted of amniotic fluids from pregnancies yielding IUGR fetuses whose birth weight was less than or equal to the tenth percentile for gestational age; group B consisted of amniotic fluid from pregnancies yielding infants whose birth weight was greater than the tenth but less than or equal to the 25th percentile for gestational age; group C consisted of amniotic fluids from pregnancies yielding infants whose birth weight was greater than the 25th but less than or equal to the 75th percentile for gestational age. The mean 3MH:CR x 10 for groups A, B, and C were 15.9 ± 1.9, 5.4 ± 0.8, and 6.2 ± 0.5, respectively. The mean 3MH:CR x 10 was statistically different between groups A and B (P < .001) and between groups A and C (P < .001), but not statistically different between the 2 control groups. Employing an upper limit of normal of 8 for the 3MH:CR x 10,13 of 15 IUGR neonates were correctly identified as IUGR, and 23 of 27 neonates were correctly identified as being of normal birth weight for gestational age (sensitivity 86.7%, specificity 85.2%, incidence of correct diagnosis 85.7%). No consistent relationship was shown to exist between maternal serum and amniotic fluid 3-methyl histidine level. There was no statistically significant relationship between 3MH:CR x 10 and gestational age. The comparison of the data generated in this study to that obtained with previously reported ultrasonic and biochemical techniques suggests that the amniotic fluid 3MH:CR ratio may prove helpful in establishing the antenatal diagnosis of IUGR, particularly in cases where the gestational age is uncertain.