Premature rupture of membranes refers to the rupture of the membranes before the onset of labor, followed by the leakage of amniotic fluid. It is necessary to distinguish premature rupture of membranes from increased vaginal discharge and urinary incontinence. The methods to diagnose premature rupture of membranes include the following aspects: First, symptomatically, after the rupture of membranes, a clear liquid intermittently leaks from the vagina, accompanied by mild abdominal pain or bloody show. Second, after the rupture of membranes, the liquid leaking from the vagina can be tested with pH paper, which in most cases will change color, confirming the diagnosis of premature rupture of membranes. Third, an ultrasound can be used to observe a reduction in the amount of amniotic fluid within the amniotic cavity. Fourth, the leaking fluid can be examined under a microscope to observe "fern-like" crystallization, which can also confirm the diagnosis of premature rupture of membranes.