When the water breaks without stomach pain, it is considered to be caused by premature rupture of membranes, and its causes include reproductive tract infection, elevated pressure in the amniotic cavity, uneven stress on the membranes, trauma, and nutrient deficiencies. 1. Reproductive tract infection: infection is the main cause of premature rupture of membranes, pathogens are commonly found in anaerobic bacteria, chlamydia, group B streptococcus and Neisseria gonorrhoeae, etc. The pathogens can upwardly invade the local membranes of the endocervical os, which can lead to the decrease of the local tension of the membranes, and cause premature rupture of membranes. 2. Elevated pressure in the amniotic cavity: the fetal membranes covering the cervix have morphological, biochemical and histological changes in the late stage of pregnancy, which is a weak area. Twin pregnancy or excessive amniotic fluid can lead to high pressure in the uterine cavity, thus leading to rupture of the fetal membranes. 3. Uneven pressure on the fetal membranes: abnormal fetal position, cephalopelvic asymmetry, etc., can lead to premature rupture of the fetal membranes because the exposed part of the fetus can’t connect with the pelvic inlet and the pelvis is empty, resulting in the amniotic sac being subjected to uneven pressure. 4. Trauma: improper puncture of the amniotic cavity, artificial stripping of membranes, sexual stimulation, etc., can cause premature rupture of membranes. 5. Nutritional deficiencies: such as pregnant women in the pregnancy diet is not appropriate, resulting in copper, zinc, vitamin C and other nutrients, can affect the synthesis of collagen fibers, elastic fibers of the membranes, prompting a decline in the tensile capacity of the membranes, causing premature rupture of the membranes. Once the phenomenon of amniotic fluid rupture, we should pay attention to timely hospital consultation, active treatment, so as not to delay the condition.