Determining a threshold for amniotic fluid as a predictor of perinatal outcome at term

Abstract

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.

Keywords::

• Amniotic fluid
• fetal vulnerability index
• oligohydramnios

Declaration of Interest: The study is supported in part by a University Research Foundation grant from the University of Pennsylvania to Dr. Odibo and an Anderson Trust Fund grant at Lehigh Valley Health Network to Dr. Quiñones. Presented at the 31st Annual Meeting of the Society for Maternal-Fetal Medicine, February 12, 2011, San Francisco, California.