Reference range for amniotic fluid index measurements in a Brazilian population.

OBJECTIVE

The aim of this study was to determine the reference range for amniotic fluid index (AFI) measurements in a large sample of the Brazilian population.

METHODS

This was a retrospective cross-sectional study on 3837 normal singleton pregnancies between 18+0 and 38+6 weeks of pregnancy. The AFI was measured from the largest vertical pockets of amniotic fluid in the four quadrants of the uterine cavity. To assess the correlation between AFI and gestational age (GA), polynomial equations were calculated, with adjustments using the determination coefficient (R2).

RESULTS

The mean maternal age and gestational age were 27.01±6.57 years and 30.43±5.29 weeks, respectively. The mean AFI ranged from 12.2±2.6 cm at 18 weeks to 11.6±6.0 cm at 38 weeks of pregnancy. The correlation between AFI and GA was best represented by a linear equation: AFI=17.78-0.153*GA (R2=0.027).

CONCLUSION

We established the reference range for the AFI in a large sample of the Brazilian population. This reference range can be used to monitor deviations in the volume of amniotic fluid in fetuses at high risk for intrauterine growth disturbances.