Normal ultrasonic evaluation of amniotic fluid in low-risk patients at term

To study women at the time of admission to the labor and delivery unit to determine which type of ultrasonographic assessment of the amniotic fluid--amniotic fluid index (AFI), single deepest vertical pocket (DVP) or amniotic fluid distribution (AFD)--had the greatest clinical utility in predicting labor complications.

Patients not at term, with a nonvertex presentation, or with ruptured membranes, polyhydramnios, or known maternal or congenital abnormalities were excluded. We included 266 low-risk pregnant women admitted for labor. Medical charts were reviewed for documentation of meconium-stained amniotic fluid (Mec), cesarean section (C/S) for fetal indications and admissions to the neonatal intensive care unit (NICU). Sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for AFI, DVP and AFD were calculated in relation to the three outcome variables. Positive findings were defined as: AFI < 5.0, DVP < 2.5 cm and AFD, sum of the two lower quadrants of the AFI with a lower value than the sum of the two upper quadrants.

Mec was documented in 56 patients (21%), 13 patients (4.8%) had a C/S for fetal indications, and 4 infants (1.5%) were admitted to the NICU. Abnormal AFI was detected in 35 patients (13%), abnormal DVP in 38 patients (14%) and abnormal AFD in 117 patients (44%). PPV and NPV for prediction of Mec, C/S and NICU were: Mec 31% and 80% for AFI, 26% and 80% for DVP; 31% and 91% for AFD; C/S 8.6% and 95% for AFI, 5% and 95% for DVP; 8.6% and 100% for AFD and NICU, 0% and 98% for AFI, 0% and 95% for DVP, and 2.7% and 99% for AFD.

Normal ultrasonographic values for AFI and AFD are associated with a very low risk of labor complications.