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Determining a threshold for amniotic fluid as a predictor of perinatal outcome at term
Joanne N Quiñones1, Anthony O Odibo, Marilyn Stringer
1Division of Maternal Fetal Medicine, Department of Obstetrics and Gynecology, Lehigh Valley Health Network, Allentown, PA 18105, USA. joanne_n.quinones@lvhn.org
Objective:
To determine a threshold level of amniotic fluid in low-risk term pregnancies predictive of adverse perinatal outcome.
Methods:
Prospective cohort study of low-risk patients at term undergoing amniotic fluid volume measurement. Amniotic fluid index (AFI) remained blinded unless ≤ 1 cm or ≥ 25 cm. Primary outcome was a positive fetal vulnerability index (FVI). The last AFI was evaluated as predictor of a +FVI. We estimated that we needed to perform ultrasounds on 620 women.
Results:
Patients were enrolled through 2004-2008. There were 24 (7.8%) patients delivering a neonate with +FVI. An AFI < 8 cm increased the risk of a +FVI (risk ratio 2.70 [95% CI 1.2, 6.0]; p = 0.01); however, the area under the receiver operating characteristics curve was 0.60. Enrollment was stopped at 308 patients due to enrollment challenges.
Conclusions:
An AFI cutoff <8 cm was associated with an increase in FVI outcomes but had a low positive predictive value for a +FVI. Isolated incidentally found low fluid in uncomplicated pregnancies may not be an indication for immediate intervention.
