Ultrasonographic determination of amniotic fluid volume in normal pregnancy.

ABSTRACT

Ultrasonographic assessment of amniotic fluid has important implications because documentation of abnormalities of amniotic fluid volume may provide valuable information to enhance fetal health assessment. But in our country no study was conducted to establish normal values of amniotic fluid volume. So, this study was designed to find out normal values of amniotic fluid volume at various stages of gestation. The study was conducted in the department of Radiology and Imaging, BIRDEM in collaboration with the department of Obstetrics and Gynaecology, BIRDEM from 1(st) July, 2001 to 30(th) June, 2002. One hundred and twenty patients of normal pregnancy between 15 to 38 weeks' gestation were scanned by ultrasonography and their amniotic fluid volume was measured. For each gestational age between 15 and 38 weeks, 5 patients were recruited, and only one examination was done per pregnancy. Currently, the three semi-quantitative methods of assessing amniotic fluid volume include the amniotic fluid index (AFI), single deepest pocket (SDP) and two diameter pocket (TDP). Amniotic fluid volume of the study population was measured by the three methods. The values were plotted against each week in tabulated form. Thus the normal range of amniotic fluid volume in three methods (AFI, SDP, TDP) across gestational age in normal pregnancies was established. The mean value of amniotic fluid volume in AFI, SDP and TDP were 13.224 cm, 4.679 cm and 19.252 cm(2) respectively. AFI and SDP showed amniotic fluid volume increased with increasing gestational age up to early third trimester, but volume decreased thereafter. The prevalence of false positive result for oligohydramnios was 0.83% for AFI, 0% for SDP and 23% for TDP. The prevalence of false positive result for hydramnios was 1.66% for AFI, 0.83% for SDP and 0% for TDP. Thus the normal values of amniotic fluid volume for each of the three ultrasonographic techniques in the perspective of our country were obtained from the study. As the study was conducted with a limited number of patients, further study may be carried out with a large number of observations to reevaluate the results of the study.