To diagnose premature rupture of membranes, first, a pH test of the vaginal fluid must be conducted. The normal pH value of vaginal fluid in women ranges from 4.5 to 5.5, whereas the pH of amniotic fluid ranges from 7.0 to 7.5. If the membranes have ruptured prematurely, the pH value would be greater than 6.5. Additionally, a smear test of the vaginal fluid can be done by placing vaginal secretions under a glass slide and examining them under a microscope. If fern-like crystals are observed, this indicates the presence of amniotic fluid. Furthermore, an ultrasound examination can be conducted. If the ultrasound shows a rapid decrease in the amount of amniotic fluid, this can assist in the diagnosis.