Objective: To determine whether low amniotic fluid index (AFI) reflects an increase in cord blood erythropoietin levels and is a marker of antenatal fetal hypoxia in small for gestational age (SGA) and appropriate for gestational age (AGA) fetuses in the third trimester.
Methods: Erythropoietin levels in cord blood were measured in 134 high-risk obstetric patients, including 40 with low AFI (7 cm or less) and 94 with normal AFI (greater than 7 cm), which were sampled at elective cesarean delivery of fetuses with a gestational age of 32 to 39 weeks. The infants were divided into the SGA and AGA groups based on birth weight. Partial correlations of AFI with cord blood erythropoietin levels were evaluated by Pearson correlation coefficient after logarithmic transformation of erythropoietin levels in each group.
Results: Cord blood erythropoietin levels in SGA fetuses with low AFI (n = 24) were significantly higher than those in SGA fetuses with normal fluid volume (n = 16) (171.6 +/- 207.4 mIU/dL compared with 36.1 +/- 24.1 mIU/dL, P < .001). Conversely, cord blood erythropoietin levels in AGA fetuses with low AFI (n = 16) were not significantly different than those in AGA fetuses with normal fluid volume (n = 78) (32.1 +/- 18.7 mIU/dL compared with 29.5 +/- 15.3 mIU/dL). A significant partial correlation between AFI and erythropoietin levels was demonstrated only within the SGA group (P < .001, r = -.67).
Conclusion: Low AFI could indicate the degree of antenatal fetal hypoxia in SGA fetuses. The impact of a reduced amniotic fluid volume on antenatal fetal condition might be less severe in AGA fetuses than in SGA fetuses.