Prelabor rupture of membranes: Clinical sciences

Prelabor rupture of membranes or PROM is the spontaneous rupture of membranes that occurs before the onset of labor. Term PROM occurs when membranes rupture at 37 weeks of gestation or later whereas preterm PROM or PPROM occurs before 37 weeks. Membrane rupture prior to labor at term may be due to a normal physiologic weakening of membranes, whereas preterm PROM may have a variety of pathologic causes, such as intraamniotic infections. The management of PROM is based on gestational age as well as maternal and fetal status.

Your first step in evaluating a patient presenting with a chief concern suggesting PROM is to assess their CABCDE and conduct a primary obstetric survey to determine if they are stable or unstable. If the patient is unstable, you should immediately control any hemorrhage. Always keep in mind that patients with PROM are at an increased risk of placental abruption, which can lead to hemorrhage. Then, stabilize their airway, breathing, and circulation. Additionally, obtain IV access; type and cross if packed RBCs are needed; continuously monitor maternal vital signs; and consider intubation when appropriate.

Next, monitor the fetal heart rate and perform your primary obstetric survey. Perform a sterile speculum examination to visually check cervical dilation and assess for rupture of membranes or ROM. Evidence of membrane rupture includes visualizing amniotic fluid from the cervix; pooling of amniotic fluid in the vagina; or ferning of the fluid on microscopic examination.

Another quick test you can do is a pH test. Amniotic fluid is more alkaline than the vaginal environment. If PROM has occurred, the fluid sampled from the vagina will turn nitrazine paper, or pH strips, a blue color that indicates a basic pH between 7.1 to 7.3. That being said, the pH test isn’t perfect, and false positive results from the presence of blood, semen, alkaline antiseptics, or bacterial vaginosis may occur. A false negative result may also occur if there’s minimal remaining amniotic fluid following rupture.

Here’s a clinical pearl! To test for ferning, use a sterile swab to obtain a sample of fluid from the vagina. Then, smear it onto a microscope slide, let it dry, and examine under a microscope; if you see fern-like or snow-flake-like crystals, that’s a positive fern test.

Alright, once these important steps are done, perform a physical exam to evaluate for life-threatening fetal conditions. The prime example is a prolapsed umbilical cord, which can happen with ruptured membranes when the presenting part of the fetus is not well engaged with the cervix. In this case, fetal heart tracing shows bradycardia, defined as a heart rate of less than 110.

On exam, you’ll see an umbilical cord passing through the cervix into the vagina or across the cervix. If you see this, immediately insert your hand into the vagina to elevate the presenting fetal part off of the umbilical cord and roll to the operating room for an emergency cesarean delivery!

Okay, let’s move on to stable patients. Your first step here is to obtain a focused history and physical exam. Patients usually report leakage or a sudden gush of fluid from the vagina. History might also reveal intermittent contractions, mild vaginal bleeding, or fever. You can also assess risk factors that may predispose a patient to PROM, like a history of preterm PROM in a previous pregnancy, low BMI, low socioeconomic status, and cigarette or illicit drug use.

On a sterile speculum exam, you may observe a short cervix or cervical dilation. Look for signs that confirm rupture of membranes, including visualization of amniotic fluid from the cervix, fluid pooling in the vagina, ferning on microscopic examination, or a basic pH of vaginal fluid between 7.1 to 7.3. If you see these findings, diagnose PROM. Then, start inpatient assessment and evaluate for intraamniotic infection by obtaining a maternal temperature, fetal heart tracing, and CBC.

An intraamniotic infection is suspected if there is a one-time maternal temperature of at least 39 degrees Celsius, OR if there is a temperature between 38.0 and 38.9 degrees Celsius and at least one of the following: fetal tachycardia, meaning a fetal heart rate above 160; maternal leukocytosis, with a white blood cell count above 15,000; or the presence of purulent fluid from the cervical os. If the patient meets either of these criteria, suspect an intraamniotic infection, start IV broad-spectrum antibiotics, and proceed with delivery.

If the patient has no signs or symptoms of intraamniotic infection, assess their gestational age to determine the management of PROM.

Okay, let’s talk about patients less than 23 weeks of gestation with PROM, where the fetus is considered previable. The main treatment here is outpatient expectant management and pelvic rest. You can offer outpatient monitoring with close surveillance in patients who are clinically stable until viability. Be sure to have your patient check their temperature and call if they have any signs of infection, labor, or bleeding. Counsel the patient on realistic neonatal outcomes as well as risks of expectant management, including intraamniotic infection, endometritis, placental abruption, sepsis, transfusion, hemorrhage, and readmission.