Tests for Diagnosing Ruptured Membranes (Rupture Amniotic Sac)

The most common tests for diagnosing ruptured membranes are the pH test and the Nitrazine test.

The pH test involves sampling vaginal fluid  for pH.

 Normal pH for vaginal fluid is between 4.5 and 5.5

Normal pH of amniotic fluid usually falls between 7.0 and 7.5.

 If the sample of the vaginal fluid is more alkaline than normal vaginal pH, then it is likely that the membranes have ruptured and amniotic fluid has leaked into the vagina.

The Nitrazine test

involves placing small amounts (a drop or two) of vaginal fluid onto the pH test strips prepared with Nitrazine dye. A chemical reaction occurs and the strips change color, indicating the pH of the vaginal fluid. If the color shows the pH is greater than 6.5, it’s likely the membranes have ruptured.

False readings:

False readings can occur with:

  1. blood-tinged mucus, blood has a pH closer to amniotic fluid than vaginal fluid.
  2. vaginal infections can increase the pH of fluid in the vagina
  3. recent intercourse may increase vaginal pH due to the high pH of semen has a high pH.
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