The amniotic fluid test paper turns blue. In the case of premature rupture of membranes, the vagina is peered at clinically with a speculum to see if there is a pool of amniotic fluid in the posterior fornix, and then the amniotic fluid is checked with a PH test paper. If the PH test paper turns blue, premature rupture of membranes is considered; if the PH test paper does not turn blue, further observation is needed. Because the normal vaginal environment of pregnant women is acidic and amniotic fluid is alkaline fluid, when the membranes rupture prematurely, the amniotic fluid enters the vagina and the amniotic pool in the posterior fornix is alkaline fluid. At this time, use PH test paper to test, if it turns blue, it suggests that the pool of fluid in the posterior fornix is amniotic fluid. Therefore, if the test with amniotic fluid test paper is blue, it is considered that premature rupture of the membranes has occurred. However, it is also affected by other factors, such as cervical mucus and blood, which are alkaline fluids and can affect the results of the PH test paper.