Amniotic fluid volume in normal pregnancy: comparison of two different normative datasets

The aim of the present study was to compare the two normative datasets of amniotic fluid volume (AFV).

The similarity of the two datasets to classify AFV as oligohydramnios, normal, and polyhydramnios based on fixed cut-offs, stratified by gestational ages (<24 weeks, 24-33(6/7), 34-36(6/7) , and >37 weeks, and to identify oligohydramnios/small for gestational age (SGA) and polyhydramnios/large for gestational age (LGA) was evaluated.

Of the 209 pregnancies assessed, the AFV was 94 ≤ 500 mL, 101 between 501 and 1999 mL, and 14 ≥ 2000 mL. The datasets were in agreement classifying the AFV as oligohydramnios, normal, and polyhydramnios in 76% of the pregnancies. Brace classified more overall patients with oligohydramnios (19%) versus Magann (3%) (P < 0.001). In term pregnancies (>37 weeks), Brace was more likely to classify pregnancies with oligohydramnios (15%) than Magann (3%) (P = 0.004). The likelihood ratio (LR) to detect oligohydramnios/SGA was greater with Magann (LR 12.9) versus Brace (LR 2.75).

The two datasets classify AFV differently in 24% of cases. Brace's dataset is more likely to categorize patients as having oligohydramnios and Magann's dataset is a more useful test for oligohydramnios/SGA identification.