(Preterm) Premature Rupture of Membranes
last authored: Dec 2012, David LaPierre
last reviewed:
Introduction
Normally, rupture of membrane (ROM) occurs spontaneously after or with the onset of labor close to term delivery. Premature rupture of membranes (PROM) occurs prior to onset of labor when the fetus is over 37 weeks gestation; if ROM occurs under 37 weeks, it is termed preterm premature rupture of membranes (PPROM). Rupture is prolonged if it persists for more than 24 hours prior to the onset of labor. Both PROM and PPROM result in increased risk to mother and baby.
PROM occurs in 10% of all pregnancies, 8% occur at term and 2-3.5% at preterm pregnancies. It is responsible for almost 1/3 of preterm births. Almost 90% of woman who are at term will go into labor 24 hours after PROM. Of women with PPROM, approximately half will go into labour within 24 hours, and 70-80% will begin labour within one week.
Unlike in term infants, the risk of amniotic infection among premature does not increase with the time interval between rupture and birth. This is true when the infection is already present at the time of ROM and the infection itself could have triggered the onset of labor.
The Case of Mrs H
Mrs. H presents to Labour and Delivery at 33 weeks gestation, concerned that 'her waters might have broken".
- what do you ask Mrs H?
- what do you examine?
- what lab tests are possible to determine if her membranes have ruptured?
- what treatment should be offered her, if any?
Pathophysiology
Normally, cells of amniotic membrane are programmed to die at term. Cell death activates collagenase, a catabolic enzyme that leads to degradation of the membranes.
Mechanical forces contributed by the descending foetus/foetuses add to ROM. This same process probably occurs in PPROM, only prematurely.
Some pathologic factors such as infection cause inflammation of the membranes and increase the likelihood of damage. However, infection in some cases may be a consequence of PPROM and not its cause.
Causes and Risk Factors
Causes for PROM and PPROM include:
- idiopathic (if no other cause is found)
- infection, eg bacterial vaginosis, sexually transmitted infection, or urinary tract infection
- amniocentesis during amniotic fluid analysis
- cervical insufficiency or cerclage (as a treatment)
- cervical treatment (laser, LEEP)
- placental abruption
- uterine distension (multiple gestation, polyhydramnios)
Risk factors include:
- previous PROM
- previous preterm birth
- tobacco use
- poor socioeconomic status
- low body mass index
Signs and Symptoms
- history
- physical exam
History
A careful history is important in determining likelihood of PROM or PPROM.
Take note of:
- amount of fluid from the vagina
- timing: was there a gush that occurred with laughing or coughing?
- odour: foul-smelling?
- persistence of flow: has there been a steady trickle?
- colour: check for turbidity and meconium or blood staining
Physical Exam
Vitals of mother and baby should be taken, with particular attention to:
- maternal fever
- fetal heart rate
Digital exam should be avoided due to risk of ascending infection.
Sterile speculum exam is helpful for a number of reasons:
- assess pooling in the posterior fornix
- flow of fluid from the cervix, especially when coughing
- ferning (see under 'labs' below)
- Nitrazine paper test (see under 'labs' below)
Investigations
- lab investigations
- diagnostic imaging
Lab Investigations
Assess for GBS status. In a woman who has had preterm birth, screening for bacterial vaginosis is indicated.
Rupture of membranes may be assessed in a number of ways via sterile speculum exam:
Visual inspection includes looking for pooling in the posterior fornix. Asking the woman to cough (Valsalva maneuver) may allow visualization of amniotic fluid leaking from the cervical os.
Ferning
Sample fluid from posterior fornix and place on slide; let air dry for 10 minutes and examine, unstained, under a microscope.
Nitrazine swabs
Sample fluid from posterior fornix. Normal vaginal pH is 4.5- 6.0. Amniotic fluid pH is 7.1 - 7.3. False positive tests can occur with blood, vaginal infections, alkaline urine, and semen. High negative predictive value
Fetal fibronectin
Helpful between 24-34 weeks to predict risk of preterm labour.
Place in the posterior fornix for 10 seconds. Wait 30-120 minutes for result.
Predictor of preterm deliver in 7-14 days.
- high NPV
- low PPV
Contraindications:
- anything in the vagina within 24 hours (including sexual intercourse and digital exam)
- GA above 34 weeks
- bleeding
- cervix dilated greater than 3 cm
CBC
A high WBC count with dominance of neutrophils may suggest intra-uterine infection, eg chorioamnionitis. The evidence to support the use of CRP for the early diagnosis of chorioamnionitis remain unclear, but a high CRP level may give weight to this diagnosis.
Diagnostic Imaging
Fetal ultrasound may be carried out for:
- biophysical profile and scoring assessment of fetal well-being and growth
- gestational aging and ruling out multiple gestation
- estimation of fetal weight
- identification of placental placement
- assessing for abruption
- screening for congenital anomalies
Transvaginal ultrasound can be done to measure cervical effacement.
<2.5 cm under 28 weeks suggests increased risk of preterm birth.
advantages
- quite noninvasive
- quick and easy
- good inter-rater reliability
disadvantages
- not available everywhere
- need training to do
Differential Diagnosis
The differential for rupture of membranes includes:
- urine
- leukorrhea
- infection (candidiasis, trichomoniasis, vaginosis)
Treatments
If a woman who is at risk for cord prolapsed (ie known absence of head engagement) ruptures her membrane; there is a high risk of cord prolapse. This woman should call for help, position herself on hands and knees, and be urgently evaluated for prolapse.
Management of PROM and PPROM includes:
- confirming and documenting diagnosis
- assessing mother (vitals, physical exam) and fetal well-being (nonstress-test)
- assessing position and presentation; absence of head presentation increases risk of cord prolapse
- ultrasound for biophysical profile: determining amniotic fluid index
- identifying and treating any predisposing factors
- avoiding digital examinations when possible (less important if woman is in active labour)
- prophylactic antibiotics, regardless of whether GBS status is known
- screening for urinary tract infections, sexually transmitted infections, and group B streptococcus carriage, and treated with appropriate antibiotics if positive
- treating herpes simplex virus infection if present
- surveillance, including maternal vitals, fetal monitoring, uterine irritability, and WBC
Corticosteroids should be given to mature lungs at 24-34 weeks of gestation. A single course of antenatal corticosteroids should be administered to women with PROM before 32 weeks of gestation to reduce the risks of respiratory distress syndrome (RDS), perinatal mortality, and other morbidities. The efficacy of corticosteroid use at 32–33 completed weeks is unclear based on available evidence, but treatment may be beneficial particularly if pulmonary immaturity is documented.
Induction vs Expectant Management
Expectant management reduces risk of prematurity but increases risk of intraunterine infection.
PROM: Induction of labour (with oxytocin or prostaglandin) is recommended for term pregnancies, using oxytocin or prostaglandin.
PPROM 34-37 weeks: induction is recommended
PPROM < 34 weeks: expectant management is usually preferred, with efforts to prolong pregnancy. Important considerations include:
- daily fetal monitoring
- antibiotic prophylaxis
- fetal lung maturity, tested via pooled fluids and increased using 1-2 doses beta methasone
- tocolytics, in some situations
- transfer to a health facility equipped to care for premature where both mother and fetus can be safely and closely monitored
- home care for a viable fetus at < 32 weeks with PPROM has not been been established.
For PPROM < 32 weeks: delivery is delayed until 33 completed weeks as long as there are no maternal or fetal complications;
- induce if fetal lung maturity has been established
- Group B Streptococcal prophylaxis and other antibiotics to prolong latency if no contraindications
- there is no consensus regarding the use of corticosteroids for lung maturity and, therefore, can not be recommended.
Provide GBS prophylaxis if status is unknown.
Consequences and Course
Complications from PROM include:
- fetal or maternal infection
- umbilical cord prolapse
Complications of PPROM include:
- preterm labour and delivery
- fetal or maternal infection
- umbilical cord prolapse
- severe oligohydramnios: pulmonary hypoplasia or fetal deformity
Resources and References
Practice bulletins No. 139: premature rupture of membranes. Obstet Gynecol. 2013 Oct;122(4):918-30.
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