The influence of fetal position on amniotic fluid index and single deepest pocket.
OBJECTIVE
To evaluate the effect of fetal position on measurement of amniotic fluid index (AFI) and of the single deepest pocket (SDP).


METHODS
This was a prospective observational study, in a university obstetric unit, of women with an uncomplicated singleton pregnancy with longitudinal lie and cephalic presentation at or beyond 28 weeks of gestation. AFI was calculated and SDP measured and the fetal position was characterized in terms of three parameters. These were: the side of the maternal abdomen on which the fetus lay; a numerical representation (laterality score) of the distance that the fetus was from the sagittal midline plane of the maternal abdomen; the orientation of the fetal trunk (ventral anterior, lateral or posterior).


RESULTS
Eighty-one women were recruited into the study. There was a significant relationship between the laterality score and the AFI (P = 0.005) but not the SDP (P = 0.23): AFI was on average 4.35 cm higher in fetuses lying centrally compared with those lying laterally inside the uterus. There was no significant difference for either SDP (P = 0.8) or AFI (P = 0.3) between fetuses lying on the right or the left side of the maternal abdomen. Similarly, there was no significant difference in SDP (P = 0.9) or AFI (P = 1.0) for the different orientations of the fetal trunk.


CONCLUSIONS
Fetal position affects the measurement of AFI but not that of SDP. Therefore, SDP may be a more consistent parameter for the estimation of amniotic fluid volume.
Fok
W Y
WY
Department of Obstetrics and Gynaecology, Prince of Wales Hospital, The Chinese University of Hong Kong, Hong Kong. angelfok@cuhk.edu.hk
Chan
L Y
LY
Lau
T K
TK
D000005:Abdomen / Q000000981:diagnostic imaging; D000328:Adult; D000653:Amniotic Fluid / Q000000981:diagnostic imaging*; D005260:Female; D005333:Fetus / Q000196:embryology*; D005865:Gestational Age; D006801:Humans; D007746:Labor Presentation; D011247:Pregnancy; D011446:Prospective Studies; D016216:Ultrasonography, Prenatal