Comparative efficacy of two sonographic measurements for the detection of aberrations in the amniotic fluid volume and the effect of amniotic fluid volume on pregnancy outcome

Abstract

Objective: To determine in pregnant women with preterm labor the relative efficacy of the amniotic fluid index (AFI) and the two-diameter pocket to detect abnormalities in amniotic fluid volume (AFV), and to relate these findings to pregnancy outcome.

Methods: Fifty-seven healthy women with preterm labor underwent amniocentesis in the third trimester to detect subclinical chorioamnionitis and assess fetal lung maturity. The AFV was estimated by the AFI and two-diameter-pocket methods, then confirmed by a dye (aminohippurate sodium)-dilution technique. Each labor was evaluated for severe variable decelerations requiring amnioinfusion, fetal distress resulting in cesarean delivery, and a 5-minute Apgar score below 7.

Results: Using fluid volume confirmed by dye dilution, the AFI correctly diagnosed AFV as low (less than 500 mL) in only two of 23 (8.7%) patients, compared to 14 of 23 (61%) for the two-diameter pocket (P < .001). Fetal distress requiring cesarean delivery occurred significantly more often in the hydramnios group (three of six) compared to those with normal AFV (one of 23) (P < .03), and approached significance in the oligohydramnios group (two of 21) (P = .056). There were no significant differences among the three patient groups regarding the need for amnioinfusion for severe variable decelerations or the occurrence of 5-minute Apgar scores below 7.

Conclusions: Compared to the AFI, the two-diameter pocket is a superior sonographic measurement for the detection of oligohydramnios. In an otherwise low-risk pregnancy with preterm labor, oligohydramnios is associated with no greater risk for an adverse outcome than is a normal AFV.