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To distinguish between amniotic fluid due to membrane rupture and normal vaginal secretions in patients beyond the 20th week of pregnancy who present with spontaneous vaginal fluid passage. Characteristic arborization, or typical ferning pattern, confirms amniotic fluid and spontaneous membrane rupture.


Sterile speculum, vaginal fluid, microscope slide, microscope, and sterile swab or pipette.


  1. Place patient in dorsal lithotomy position.

  2. Do not use lubricants or cleaning agents.

  3. Place sterile speculum into vaginal vault.

  4. Obtain sample of vaginal secretions from posterior vaginal pool using a pipette or sterile swab.

  5. Place a drop of vaginal fluid on a microscope slide.

  6. Spread the specimen evenly so that a thin smear is formed.

  7. Allow the fluid to air dry for 5 to 10 minutes. Do not apply heat.

  8. Examine slide under low power (10×) for ferning pattern.

FIGURE 25.27

Ferning Pattern. The arborization pattern found when a drop of amniotic fluid is allowed to air dry on a microscope slide, known as ferning. (Photo contributor: Robert Buckley, MD.)

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