The ferning and nitrazine tests of amniotic fluid between 12 and 41 weeks gestation

Most studies investigating the usefulness of ferning and nitrazine methods for detecting the presence of amniotic fluid following ruptured amniotic membranes have employed samples from vaginal pooling. Reported accuracies are 84 to 100% for the ferning test and 87 to 97% for the nitrazine test. Our study was designed to determine if these tests are applicable throughout gestation. Samples were obtained from amniocenteses between 14 and 42 weeks. Part I: Of 112 samples allowed to dry on a slide for 3 minutes only, 86.6% were ferning positive and 100% were nitrazine positive. Flame-drying increased the presence of ferning to 96.4%. Part II: 363 samples were allowed to dry completely for up to 10 minutes. All samples were ferning and nitrazine positive. Part III: 17 samples were tested for ferning and nitrazine at 1 hour, and again at 1 week. Sixty-six samples were tested within 1 week and again at 2 weeks. All samples remained ferning and nitrazine positive. Therefore optimal analysis of suspected amniotic fluid occurs when specimens are air-dried for 10 minutes. These tests may be reliably performed at gestations of 12 to 41 weeks.