AMNIOTIC-FLUID INDEX - GESTATIONAL-AGE SPECIFIC VALUES FOR NORMAL HUMAN-PREGNANCY

Amniotic fluid volume is an important parameter in the assessment of f etal well-being. The purpose of this study was to define the values of the amniotic fluid index for normal pregnancy by week of gestation in our population. The amniotic fluid index was measured prospectively i n 892 patients with a normal singleton pregnancy between 15 and 40 wee ks and an estimated fetal weight between the 10th and 90th percentile. The results were stratified by week of gestation. From a median of 10 .3 cm (range, 8.7-13.7,5th-95th percentile) at 15 weeks' gestation, th e amniotic fluid index rose progressively to a maximum median of 14.0 cm (range, 4.0-18.6) at 30 weeks. The index then gradually declined to a median of 9.1 cm (range, 4.8-14.2) by 40 weeks' gestation. The diff erence between the median index for preterm patients (11.9 cm) and tha t for the term group (10.8 cm) was found to be statistically significa nt (P<.05). The difference between the median amniotic fluid index for the total group and the medians for the preterm and term patients was also significant (P<.05). Gestational age-specific values of amniotic fluid index should be used, and the 5th and 95th percentiles serve as the lower and upper limits, respectively, of normal.