Longitudinal Measurement of Amniotic Fluid Index in Term Pregnancies and Its Association with Intrapartum Fetal Distress

OBJECTIVE: The aim of the present study was to evaluate the dynamic changes in serially obtained amniotic fluid index values and to determine any association with intrapartum fetal distress in a term population. MATERIALS AND METHODS: All patients, > or = 40 weeks of gestational age, evaluated at the Institute of Obstetrics and Gynecology, 'G. Salesi' Hospital, University of Ancona, between January 1, 1994, and December 31, 1995, participated in this longitudinal study. Women with an amniotic fluid index of > 50 mm, who also demonstrated a reactive nonstress test, underwent semiweekly amniotic fluid assessment until spontaneous labor. After 42 gestational weeks, the patients underwent an elective induction of labor. All patients were managed with continuous electronic fetal heart rate monitoring throughout labor. The incidence of intrapartum fetal distress, and meconium staining of amniotic fluid were evaluated with respect to the amniotic fluid index. RESULTS: Of the 117 patients that were evaluated by ultrasound, 83 women had multiple amniotic fluid index measurements and were enrolled in the study. A serial decrease in amniotic fluid index was documented in 54 women; the mean decrease per week was 20.7 +/- 15.4%. An increase in amniotic fluid index was noted in 17, while 11 women showed no change in amniotic fluid index over time. The 14 patients who underwent cesarean section for fetal distress had a significantly lower amniotic fluid index (p < 0.001) at the last sonographic examination than the normal outcome group. Significant differences were also observed for a serial decrease in the amniotic fluid index within a week (p < 0.001). The sensitivity and specificity of the 30% serial decrease in the amniotic fluid index cutoff point, with respect to intrapartum fetal distress were 86 and 93%, respectively. CONCLUSION: Longitudinal measurement of the amniotic fluid index seems to be an effective method in predicting intrapartum fetal distress in a term population.