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In patients who present with a complaint consistent with possible PROM, there are a number of variables that must be assessed before a plan of management can be decided on. Once the diagnosis is made, the clinician must know the fetus gestational age, if the patient is in labor, if infection is present, and if the fetus is in distress.
A correct diagnosis is essential in managing the patient with PROM. A history of a large gush of watery fluid spontaneously emerging from the patient s vagina, usually without a precipitating cause, followed by continuous and somewhat steady leakage is consistent with PROM; 90% of patients who give such a history are correct. Other, similar complaints, in the absence of PROM, may occur from urinary leakage; from excess vaginal or cervical secretions, as with lower urinary tract infections; and in association with painless dilation of the cervix (incompetent cervix). A patient who presents with a complaint suspicious for membrane rupture should be examined immediately to confirm the diagnosis.
The physical examination of a patient with PROM usually reveals a moist perineum. Aseptic vaginal examination with a speculum allows visualization of a pool of watery fluid in the posterior vault, referred to as pooling. If the initial rupture occurred long before the examination (i.e., more than 24 hours), most of the fluid may have leaked out and the vagina may only appear moist. In such cases, pressure on the uterine fundus or having the patient perform a Valsalva maneuver with simultaneous observation may reveal leakage of fluid through the cervical canal into the vagina. Amniotic fluid has a characteristic odor, but it can be masked by blood or vaginal secretions, or it can be absent if only a small amount of amniotic fluid is present.
One or more rapid bedside tests are used to confirm that the substance is indeed amniotic fluid. The method most commonly used involves testing fluid
If doubt remains with the combination of history, pooling, and Nitrazine, the fluid should be tested for ferning. A sample of fluid is collected from the vaginal fornix with a cotton-tipped applicator and then smeared on a clean slide and allowed to dry completely. This usually takes 5 to 7 minutes. After it dries, amniotic fluid creates a characteristic ferning pattern or arborization of crystals under the microscope (Fig. 17-1) . A number of contaminants, such as blood, meconium, lubricants, and heavy vaginal discharges, interfere with ferning and cause false-negative results. Insufficient fluid, after prolonged rupture of membranes or with minimal leaks, can also cause negative results. Cervical mucus also ferns, and care must be taken to avoid the cervix when collecting the sample.
Ultrasound can be used as the final confirmatory step when doubt remains. Although normal fluid volume or oligohydramnios does not refute or confirm the diagnosis independently, the information can be used in concert with the history and other laboratory tests. Other tests have been described (e.g., intraamniotic dye injections), but they add little to history, physical examination, Nitrazine, ferning, and ultrasound.
Figure 17-1 Amniotic fluid ferning
as seen under the microscope.
At the time of speculum examination, other information can be obtained as well. The cervix should be visualized in all cases to make certain that no fetal extremity or umbilical cord has prolapsed through the os. An impression of cervical dilation and effacement can be ascertained. Specimens can be collected from the cervix and vagina and cultured for gonorrhea, group B streptococci, and Chlamydia species. Culturing for other organisms adds little clinically useful information. In some premature gestations, a sample can be aspirated and submitted for fetal maturity testing. Phosphatidylglycerol is the most reliable test when using amniotic fluid that has been obtained vaginally.
In confirming the diagnosis and obtaining the other information during the aseptic speculum examination, it is critical that the examiner not add to the risk of infection. A speculum examination is not likely to increase this risk because a sterile instrument is used and placed in an already bacteria-laden vagina. An intracervical digital examination should be avoided unless the patient is in active labor and the cervix appears to be dilating. Schutte and associates found that in preterm PROM, there was no apparent relation between the interval from rupture of membranes to delivery, but as the interval from the first cervical examination to delivery increased, the incidence of neonatal infection rose dramatically.
Once the diagnosis is confirmed, it is essential to accurately determine the fetus gestational age because the management of PROM, especially in the absence of labor, differs principally with this variable. Information regarding last menstrual period, prenatal examinations,
At 32 to 36 weeks of gestation, a reasonable case can be argued for obtaining amniotic fluid for fetal lung maturity testing and then delivering the patient if maturity is assured. Amniotic fluid obtained from the vaginal pool is best tested for phosphatidylglycerol because this substance, when present, is a reliable indicator of lung maturity and is unaffected by any contaminants that are likely to be found in the vagina. Results of other tests, such as the lecithin-sphingomyelin (L/S) ratio, can be unreliable from this source. If phosphatidylglycerol is absent, amniocentesis should be performed because the L/S ratio or other tests may still be dependably relied on if any indicates maturity.
Whether or not the patient actually is in labor dictates patient management in the presence of PROM. In active labor, delivery usually is planned, and cesarean section is reserved for usual obstetric complications. Because it is desirable to avoid digital intracervical examinations, especially if the patient is not in active labor, external uterine contraction monitoring and the patient s subjective symptoms are the essential elements in identifying labor. Once regular, painful uterine contractions are established, cervical examinations can be performed; when doubt exists, repeat speculum examination can be used to establish cervical dilation. Because in most cases labor is managed expectantly, the importance of identifying labor early may be questioned. In addition to anticipating delivery, the key answer is that fetal distress, which occurs more frequently with PROM because of oligohydramnios, may occur early in labor and, in the case of premature gestations, progress rapidly. Fetal heart rate monitoring should be resumed as soon as the patient goes into labor to continually evaluate fetal well-being.
The diagnosis of intraamniotic infection (chorioamnionitis) should be made as soon as possible. The complete picture of maternal fever, tachycardia, leukocytosis, malodorous or purulent vaginal discharge, tender uterus, and fetal tachycardia usually is present only in cases of advanced or particularly virulent infections. Many of these signs, such as maternal leukocytosis, that are present in isolation are nonspecific, being caused by other, concomitant variables, such as labor. Generally speaking, the clinical diagnosis of chorioamnionitis depends on maternal fever (greater than 38°C) in the presence of PROM and in the absence of some other explanation for the elevated temperature.
There is considerable debate over the value of making the diagnosis of chorioamnionitis with other, more sophisticated diagnostic techniques before the typical clinical picture makes the diagnosis clear-cut. Data exist that once chorioamnionitis is present, the likelihood of neonatal morbidity and death increases. However, although it may be intuitively likely, it is not well established that earlier diagnosis and treatment improve neonatal outcome. Tests to establish the presence of occult or earlier infection include amniocentesis with Gram stain and culture (as well as other analyses) of amniotic fluid, maternal serum C-reactive protein determination, and fetal biophysical profile evaluation.
Amniocentesis can be performed in 50% to 90% of patients with PROM who are not in labor. In studies in which intervention did not occur on the basis of amniocentesis results, chorioamnionitis occurred in more than 80% of patients with bacteria seen on Gram stain of amniotic fluid. The correlation between amniotic fluid Gram stain and culture and neonatal infection is poor, as one might expect, because most babies remain uninfected even in the face of frank chorioamnionitis. The biophysical profile is a good predictor of fetal infection but does not correlate as well with chorioamnionitis as does amniocentesis. These two modalities may be used in a complementary manner to evaluate the patient for occult infection. In addition, they may be useful in the patient with intact or ruptured membranes who has an infection whose source is not clearly identified. C-reactive protein appears to be a more nonspecific test, similar to maternal white blood cell count, and can be used only as a supplement to other methods of evaluation.
Fetal distress, principally caused by umbilical cord compression, is an underappreciated cause of adverse outcome in patients with PROM, both in term and in preterm gestations. An initial period of extended fetal heart rate monitoring to rule out such distress followed by frequent, prolonged fetal heart rate monitoring, as well as reinstitution of continuous monitoring once labor begins, is warranted. The duration of the initial monitoring period as well as the frequency of intermittent monitoring have not been established, but it is my practice to initially monitor such patients for 12 to 24 hours. After this, if expectant management is planned, a prolonged nonstress
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