Premature rupture of membranes (PROM) refers to the spontaneous rupture of the fetal membranes before the onset of labor. When this occurs at or beyond 37 weeks of gestation, it is termed term PROM. When it occurs before 37 weeks of gestation, it is defined as preterm premature rupture of membranes (PPROM). PPROM is one of the major causes of preterm birth. The earlier PROM occurs in gestation, the poorer the perinatal prognosis. The incidence of PPROM in singleton pregnancies is 2%–4%, while in twin pregnancies it ranges from 7%–20%.
Etiology
Several common factors contribute to PROM:
Genital Tract Infections
Genital tract infections are the primary cause of PROM. Common pathogens, such as anaerobic bacteria, Chlamydia, group B streptococcus (GBS), and Neisseria gonorrhoeae, ascend to invade the cervical internal os and weaken the local integrity of the membranes, leading to PROM.
Increased Amniotic Pressure
Elevated intrauterine pressure, such as in twin pregnancies, polyhydramnios, or large fetuses, can contribute to membrane rupture.
Uneven Stress on the Fetal Membranes
Abnormal fetal presentations or cephalopelvic disproportion can prevent engagement of the presenting part, leading to uneven pressure on the amniotic sac. In cases of cervical insufficiency, the amniotic sac may prolapse into the cervix, causing uneven pressure that increases the risk of PROM.
Trauma
Traumatic factors such as improper amniocentesis, sexual intercourse, or abdominal impacts can result in PROM.
Nutritional Deficiencies
Maternal deficiencies in copper, zinc, vitamins, or other nutrients can impair the synthesis of collagen and elastic fibers in the membranes, reducing tensile strength and increasing the risk of PROM.
Other Risk Factors
A history of PPROM, mid-to-late pregnancy bleeding, shortened cervical length, low body mass index (BMI), smoking, and substance use are additional risk factors for PROM.
Clinical Manifestations
The characteristic symptom involves a sudden gush of fluid from the vagina, with increased leakage upon abdominal pressure. In cases of term PROM, vaginal examination may reveal the absence of the forewaters and an increase in fluid leakage upon upward pressure on the presenting part. Amniotic fluid may sometimes be observed with vernix or meconium. Small amounts of intermittent, uncontrollable vaginal fluid require differentiation from urinary incontinence or vaginal discharge caused by infections such as vaginitis.
Diagnosis
Diagnosis of PROM
Clinical Manifestations
PROM is suggested by patient-reported symptoms, such as vaginal fluid leakage or persistent wetness of the vulva.
Auxiliary Examinations
Speculum Examination
Fluid may be observed flowing from the cervical canal, or pooling may be detected in the posterior fornix.
Ultrasound Examination
A reduction in amniotic fluid compared with pre-rupture levels may be observed.
Vaginal Fluid pH Testing
The normal pH of vaginal secretions is 3.8–4.5, while amniotic fluid has a pH of 7.1–7.3. A vaginal fluid pH ≥6.5 supports a diagnosis of PROM, although false positives may occur due to contamination by blood, urine, cervical mucus, semen, or bacteria.
Vaginal Fluid Smear Test (Ferning Test)
Crystallization resembling a fern-like pattern on smears from posterior fornix fluid is indicative of PROM.
Biochemical Tests of Cervicovaginal Fluid
Tests for biomarkers such as insulin-like growth factor binding protein-1 (IGFBP-1), soluble intercellular adhesion molecule-1 (sICAM-1), or placental alpha microglobulin-1 (PAMG-1) have high sensitivity and specificity for diagnosing PROM. These tests are less affected by the presence of semen, urine, blood, or vaginal infections.
Diagnosis of Chorioamnionitis
Clinical Manifestations
These include:
- Maternal fever ≥38°C.
- Foul-smelling vaginal discharge.
- Fetal tachycardia (baseline fetal heart rate ≥160 bpm) or maternal tachycardia (heart rate ≥100 bpm).
- Maternal leukocytosis (white blood cell count ≥15 × 109/L).
- Uterine irritability or uterine tenderness.
The presence of maternal fever accompanied by any of the symptoms listed in points 2–5 suggests chorioamnionitis but necessitates ruling out other causes of infection.
Histopathological Examination of Placental, Membrane, or Umbilical Cord Tissues:
Pathological evidence of infection or inflammation in these tissues supports the diagnosis of chorioamnionitis.
Effects on the Mother and Fetus
Effects on the Mother
Infection
The risk of intrauterine infection increases with longer durations of membrane rupture and greater reductions in amniotic fluid volume.
Placental Abruption
Changes in intrauterine pressure following membrane rupture can increase the likelihood of placental abruption.
Increased Cesarean Section Rate
A reduction in amniotic fluid can lead to umbilical cord compression, uncoordinated uterine contractions, or fetal distress, complicating induction of labor and increasing the likelihood of requiring a cesarean section.
Effects on the Perinatal Fetus
Preterm Birth
PPROM is a leading cause of preterm birth, and the prognosis for preterm infants is closely related to the gestational age at membrane rupture and delivery.
Infection
With concurrent chorioamnionitis, neonates are at increased risk for complications such as aspiration pneumonia, intracranial infection, and sepsis.
Umbilical Cord Prolapse and Compression
When polyhydramnios or an unengaged fetal presenting part is present, the risk of umbilical cord prolapse increases at the time of membrane rupture. Subsequent oligohydramnios may result in umbilical cord compression, leading to fetal distress.
Pulmonary Hypoplasia and Fetal Compression
Earlier gestational age at rupture increases the risk of pulmonary hypoplasia. Severe or prolonged oligohydramnios may cause fetal compression, leading to skeletal abnormalities such as clubbed hands, bowing of the legs, or fetal body adhesions.
Management
Once a diagnosis of PROM is established, maternal and fetal status should be assessed to rule out complications such as infection (chorioamnionitis), placental abruption, fetal distress, or abnormal fetal presentation.
Management of Term PROM
With prolonged rupture of membranes, the risk of intrauterine infection gradually increases. Prophylactic antibiotics should be administered if the rupture exceeds 12 hours, and unnecessary frequent vaginal examinations should be avoided. In the absence of a clear indication for cesarean delivery, active induction of labor is typically pursued within 2 to 12 hours of membrane rupture. For patients with a favorable cervix, oxytocin induction is the preferred method. For patients with an unfavorable cervix and no contraindication to vaginal delivery, cervical ripening agents such as prostaglandins may be used. Close monitoring of maternal and fetal conditions is required during trial of labor. For patients with a clear indication for cesarean delivery, pregnancy should be terminated surgically.
Management of Preterm PROM
Decisions are based on gestational age, maternal and fetal condition, the level of neonatal care available locally, and the preferences of the pregnant woman and her family. If the benefits of pregnancy termination outweigh the benefits of expectant management, termination should be considered.
Time to Pregnancy Termination
For PPROM <24 weeks of gestation, fetal survival rates are extremely low, and maternal-fetal infection risks are high; induction of labor is generally appropriate.
For PPROM between 24 and 27 weeks of gestation, decisions regarding induction depend on maternal and family preferences, as well as the availability of neonatal resuscitation. Patients choosing expectant management should be fully informed of associated risks.
For PPROM between 28 and 33 weeks of gestation without contraindications for continuing pregnancy (e.g., infection, placental abruption, umbilical cord prolapse, or fetal distress), expectant management under close monitoring is recommended.
For PPROM between 34 and 36 weeks of gestation, individualized management is necessary. Termination of pregnancy is generally advised. If expectant management is pursued, careful consideration of maternal and fetal risks and benefits, as well as close monitoring, are essential. Tocolysis should not be administered after 34 weeks, and expectant management should not exceed 37 weeks. If group B streptococcus (GBS) screening is positive, expectant management is not recommended. Conditions such as confirmed chorioamnionitis, fetal distress, or placental abruption require pregnancy termination via induction or cesarean delivery.
Expectant Management Details
General Management and Monitoring
Maintenance of vulvar hygiene and avoidance of unnecessary digital cervical examinations are key. Dynamic monitoring of maternal temperature, uterine activity, maternal and fetal heart rates, and the volume and characteristics of vaginal fluid is conducted. Routine bloodwork, amniotic fluid volume assessments, fetal heart monitoring, and ultrasound examinations are performed to detect complications such as chorioamnionitis, fetal distress, or placental abruption.
Promotion of Fetal Lung Maturity
Betamethasone or dexamethasone injection is administered for pregnancies <34 weeks to accelerate fetal lung maturity.
Infection Prevention
Prophylactic antibiotics (e.g., penicillins, macrolides) help extend pregnancy duration and reduce the incidence of chorioamnionitis and neonatal infection. A typical course lasts 5–7 days. Penicillin is the first-line treatment for GBS-positive cases.
Tocolysis
For pregnancies <34 weeks, tocolytic agents are used for up to 48 hours to allow completion of corticosteroid therapy and, if necessary, transfer to a facility with neonatal intensive care capabilities. Tocolytics should not be used if infection or placental abruption is suspected.
Fetal Neuroprotection
Pregnancies <34 weeks at risk of preterm birth are administered intravenous magnesium sulfate to reduce the risk of cerebral palsy in preterm infants.
Mode of Delivery
Decision-making regarding delivery mode considers factors such as gestational age, preterm infant survival rates, the presence of oligohydramnios or chorioamnionitis, fetal tolerance of labor, and fetal presentation. Vaginal delivery is preferred if no clear indication for cesarean delivery exists. Routine episiotomy is not required during vaginal delivery, and prophylactic use of forceps or vacuum extraction is not recommended. Cesarean delivery should be pursued when indicated. Neonatal resuscitation preparations are made prior to delivery, and placental and membrane tissues are collected for pathological examination postpartum. In cases of suspected or confirmed chorioamnionitis, amniotic fluid or neonatal ear swabs are cultured.
Prevention
Perinatal health education and guidance should be strengthened, and reproductive tract infections should be actively prevented and treated. Sudden increases in abdominal pressure should be avoided. Adequate supplementation of vitamins, calcium, copper, zinc, and other nutrients is necessary. Cervical cerclage may be performed for patients with cervical insufficiency.