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Introduction ⬇

The foam stability index (FSI) test for amniotic fluid is a modification of the amniotic fluid shake test. It provides a functional measurement of FLM based on the surface tension properties of surfactant phospholipids.

Procedure ⬆ ⬇

  1. Mix a fixed amount of undiluted amniotic fluid with increasing volumes of ethanol.

  2. Shake the sample and observe for foam.

  3. Document the largest column of ethanol in which the amniotic fluid can form and support foam. This test is almost as reliable as the L/S ratio in normal pregnancies, and it appears to have a lower false-positive rate than the shake test.

Clinical Implications ⬆ ⬇

An FSI of >0.48 is termed mature; a value of <0.46 is termed immature.

Interventions ⬆ ⬇

Pretest Patient Care

  1. Explain the reason for testing and the meaning of results.

  2. Follow guidelines in Chapter 1 for safe, effective, informed pretest care.

Posttest Patient Care

  1. Review test results; report and record findings. Modify the nursing care plan as needed.

  2. Follow guidelines in Chapter 1 for safe, effective, informed posttest care.

Interfering Factors ⬆ ⬇

  1. Blood or meconium contamination can produce a false mature result.

  2. The test is not reliable for amniotic fluid collected from the vagina.

Reference Values ⬆

Normal