Four-quadrant assessment of gestational age-specific values of amniotic fluid volume in uncomplicated pregnancies.

BACKGROUND

The purpose of this study was to establish a normative scale of amniotic fluid index (AFI) throughout gestation in uncomplicated singleton pregnancies, and to identify the lower and upper limits for each gestational week.

METHODS

Four-quadrant assessment of amniotic fluid volume (AFV) was performed prospectively in 750 uncomplicated pregnancies between 16 and 43 weeks. The logarithmic transformations were used to get the data in Gaussian distribution. The means, and the 90%, 95% and 98% confidence intervals at each week of gestation were calculated from polynomial regression equation. Statistical differences in AFIs among gestational age groups were tested.

RESULTS

The amniotic fluid index observations from regression equation curve were stratified in week-specific normative curve. The variations between mean AFI of the total population and the means of the preterm, term and postdate pregnancies were statistically significant (p<0.0001). The 90%, 95% and 98% confidence limits about the mean (12.5 cm) were 5.4 to 20.6, 4.2 to 22.3, 1.8 to 25.8 cm, respectively in term gestation. The 5th and 95th percentile serves as lower and upper limits of normal, respectively.

CONCLUSIONS

Gestational age-specific values of AFI were established, determining the significant trends of changes in the AFV with gestation. The normogram may have a clinical benefit to accurate, reliable and semiquantitative diagnosis of oligohydramnios and polyhydramnios.