The effects of blood and meconium at various dilutions and pH alterations on the fern test were evaluated in an in vitro study. Thirty-six specimens of amniotic fluid across gestational ages (16 to 42 weeks) were tested. The fern test was unaffected by meconium at any concentration and by blood at dilutions of 1:10 or greater. When blood and amniotic fluid were mixed in equal amounts, ferning was not present. Arborization of amniotic fluid was unaffected by pH alterations. These findings support the clinical usefulness of the fern test for the determination of ruptured membranes, even in the presence of blood or meconium contamination, and of pH alterations.
© 1984 The American College of Obstetricians and Gynecologists