The maximal vertical pocket and amniotic fluid index in predicting fetal distress in prolonged pregnancy

To determine cut-off values for amniotic fluid volume (AFV) predictive of fetal distress in pregnancies 40 weeks or longer, assessed using both amniotic fluid index (AFI) and height of the of maximal vertical pocket (MVP).

Amniotic fluid index and MVP were evaluated in 100 women with pregnancies of 40 or more weeks and intact membranes using a 3.5-MHz linear transducer less than 1 week prior to onset of labor. Both measurements were obtained for each participant by the same obstetrician in one sitting. Oligohydramnios was defined as an AFI of 5 cm or less or an MVP of 3 cm or less. External cardiotocography was performed during intrapartum in all cases. Fetal distress was diagnosed when any one of the nonreassuring fetal heart rate pattern occurred or when the Apgar score at birth was 6 or less. The results were analyzed by the chi(2) and the t tests.

An AFI of 5 cm or less was a better predictor of fetal distress than an MVP of 3 cm or less (P=0.000). The most statistically significant cut-off values for the occurrence of fetal distress in prolonged pregnancies were an AFI of 8 cm or less (odds ratio, 7.50) or an MVP of 2 cm or less (odds ratio, 2.67). There was a significant correlation between these 2 methods (r=+0.67), with a level of significance of 0.01, as shown by the regression curve. The secondary outcome was the statistically significant association between meconium-stained liquor and fetal distress (P=0.001).

In pregnancies of 40 weeks or longer there was a risk of fetal distress when the AFV was 8 cm or less by the AFI method or 2 cm or less as measured by MVP. In such cases, intensive intrapartum monitoring should be performed to prevent fetal jeopardy.