The diagnostic methods of premature rupture of fetal membranes are: 1, vaginal fluid pH measurement, normal vaginal fluid pH is 4.5-5.5, amniotic fluid pH is low, the range is 7.0-7.5, if the vaginal fluid pH>6.5, suggesting that premature rupture of membranes is likely to be large. 2, vaginal fluid smear, take the posterior vaginal fornix fluid placed on a clean glass slice and dried microscope, microscope amniotic fluid plant-like crystals can be diagnosed. Amniotic fluid can be diagnosed, but semen and cervical mucus may cause false positives.3. Vaginal fluid biochemical examination, insulin-like growth factor binding protein-1, soluble cell adhesion factor-1, placental α1-microglobulin content is elevated, it can be diagnosed as amniotic fluid.4. Amnioscopy can be visualized directly to the prenatal part of the fetus, and it can diagnose premature rupture of membranes when it sees hairs or other parts of the fetus but not the amniotic sac.5. Ultrasound examination If the amniotic fluid decreases sharply, it can help to diagnose the rupture.