The usefulness of ultrasound assessment of amniotic fluid in predicting adverse outcome in prolonged pregnancy: a prospective blinded observational study.
OBJECTIVE
To determine whether a single ultrasound scan at or beyond 40 weeks of gestation to detect a single deepest pool of amniotic fluid <2 cm and amniotic fluid index (AFI) <5 cm is clinically useful in the prediction of subsequent adverse pregnancy outcome.


METHODS
A prospective double blind cohort study.


METHODS
A university teaching hospital delivering approximately 6000 women annually.


METHODS
One thousand and five hundred and eighty-four pregnant women at or beyond 40 weeks of gestation.


METHODS
Ultrasound assessment of liquor to detect the single deepest pool of amniotic fluid and derive the AFI at or after 40 weeks of gestation.


METHODS
Perinatal death, meconium aspiration, birth asphyxia, intervention in labour for fetal distress, a cord arterial pH <7 and admission to the neonatal unit.


RESULTS
An AFI <5 cm but not a single deepest pool <2 cm was significantly associated with birth asphyxia or meconium aspiration. An AFI <5 cm was also significantly associated with caesarean section for fetal distress in labour, a cord arterial pH <7 at delivery and low Apgar scores. Despite there being a statistically significant association with adverse outcomes the sensitivity of AFI was low at 28.6%, 12% and 11.5% for major adverse outcome, fetal distress in labour or admission to the neonatal unit, respectively.


CONCLUSIONS
The AFI is superior to a measure of the single deepest pool as an assessment of the fetus at or after 40 weeks but has a poor sensitivity for adverse pregnancy outcome. Routine use is likely to lead to increased obstetric intervention without improvement in perinatal outcomes.
Nuffield Department of Obstetrics and Gynaecology, John Radcliffe Hospital, Headington, Oxford, UK.
J M
JM
Morris
K
K
Thompson
J
J
Smithey
G
G
Gaffney
I
I
Cooke
P
P
Chamberlain
P
P
Hope
D
D
Altman
I Z
IZ
MacKenzie
D000328:Adult; D000653:Amniotic Fluid; D001238:Asphyxia Neonatorum / Q000209:etiology; D015331:Cohort Studies; D004311:Double-Blind Method; D005260:Female; D005312:Fetal Blood; D005316:Fetal Distress / Q000209:etiology; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007231:Infant, Newborn; D015931:Intensive Care, Neonatal / Q000706:statistics & numerical data; D008471:Meconium Aspiration Syndrome / Q000209:etiology; D007744:Obstetric Labor Complications / Q000209:etiology / Q000628:therapy; D011247:Pregnancy; D011256:Pregnancy Outcome; D011273:Pregnancy, Prolonged; D011446:Prospective Studies; D012307:Risk Factors; D012680:Sensitivity and Specificity; D016216:Ultrasonography, Prenatal / Q000379:methods*