Amniotic Fluid Index According to Fetal Presentation

Kim, Tae Yoon; Cho, Jae Sung; Choi, Hyung Min; Lim, Young Koo; Kim, Kyung Soo; Lee, Yeun Hae; Kwon, Hye Kyung; Park, Yong Won; Kim, Jae Wook

Abstract

OBJECTIVE
To evaluate the effect of fetal presentation to the measurement of amniotic fluid index(AFI) in singleton pregnancy after 20 weeks of gestation.
MATERIALS AND METHODS
Review of the medical and ultrasonographic records from 1992 to 1996 including AFI value and pregnancy outcomes was performed retrospectively. The inclusion criteria were (1) singleton pregnancy delivered after 37 weeks of gestation, (2) birth weight between 10th and 90th percentile, (3) no fetal anomaly, (4) 5 minute Apgar score>or=7, (5) no maternal medical disease such as hypetensive disorders or diabetes, (6) and intact amniotic membranes at the time of ultrasonography. The results of 7,362 tests from 5,607 pregnancies were reviewed and analyzed.
RESULTS
In normal pregnancies after 20 weeks of gestation, the AFI value showed the peak during 25~30 week and decreased thereafter. The range of AFI during preterm pregnancy(30~36 weeks, N=2,836) were between 9.4 and 21.8 cm(5th to 95th percentile, mean value of 15.2+/-4.1cm). The range of AFI at term(37~40 weeks, N=1,245) were 7.7 and 21.9 cm(5th to 95th percentile, mean value of 14.2+/-4.5cm), which showed significant difference (p=0.000) from that of preterm. The range of AFI after 41 weeks(N=75) were within 4.3 and 26.7cm(5th to 95th percentile, mean value of 13.8+/-6.3cm), which showed gradual decrease. The AFI among the gravidas with breech presentation showed similar values between 20~36 weeks. At term pregnancies(after 37 weeks, N=84) with breech presentation, the AFI(range 5.2cm~22.3cm, mean value 13.5+/-4.8cm) was smaller than those with cephalic presentation, but statistically insignificant(p=0.103). The commonly used criteria for oligohydramnios, AFI 5.0cm, equated to 1st percentile in cephalic presentation and 5th percentile in breech pregnancies, respectively.
CONCLUSION
In this study AFI throughout pregnancies after 20 week of gestation showed difference of distribution of AFI according to gestational age and fetal presentation in term pregnancy. Further studies would be required to establish the cutoff value of oligohydramnios in cephalic and breech presentation at term pregnancy to establish different criteria according to fetal presentation.