Amniotic fluid index measurements during pregnancy

Amniotic fluid volume assessment has become an important part of antepartum fetal surveillance. The amniotic fluid index (AFI), or four-quadrant technique, has been suggested for this purpose. While previous reports have outlined this technique and correlated the results with pregnancy outcome, none have reviewed the changes in AFI throughout pregnancy. We studied AFI changes from 11 through 43 weeks' gestation. As part of the entry criteria, only patients with good dates were evaluated. The AFI was determined by the summation of the vertical diameter of the largest pocket in each of the four quadrants. All amniotic fluid studies were conducted using real-time linear array B-scan. During the study period, 197 patients with good dates confirmed clinically and sonographically underwent 262 AFI assessments. From 11 to 26 weeks the AFI rose progressively. Thereafter until term, the AFI remained approximately 16.2 +/- 5.3 cm. After 38 weeks the AFI appeared to gradually decline. Data obtained from this study population corroborate previously defined normal amniotic fluid volumes. These results also suggest that serial measurements of the AFI may be an effective means of assessing fetal status throughout pregnancy.