CASE: PROM at 22 weeks
J.S. is a 22-year-old woman at 22 weeks’ gestation in her second pregnancy. Her first gestation ended in spontaneous abortion at 10 weeks, followed by dilation and curettage. She has been referred to you by her midwife, who is concerned about J.S.’s complaints of loss of fluid over the past 2 weeks and who cannot document rupture of membranes by the usual means.
In your office, J.S. continues to complain of intermittent leakage of clear fluid. She says there has been no vaginal bleeding, foul-smelling discharge, fever, chills, or abdominal tenderness. You find a normal abdomen. A sterile speculum exam is equivocal, without evidence of pooling or ferning; a nitrazine test is positive, however. A complete blood count reveals no evidence of leukocytosis. Urinalysis is negative.
You suspect preterm premature rupture of membranes (PROM) when bedside ultrasonography (US) documents oligohydramnios with an amniotic fluid index of less than 5 cm. The kidneys, bladder, and stomach all appear normal.
What is the best way to confirm the diagnosis? What is the most appropriate management at this gestational age? And how do you counsel J.S. about the risk to her, and her baby, of continuing the pregnancy?
Given the very poor prognosis of many cases of early PROM, accurate diagnosis is critical to determine the best management strategy. The gold standard of diagnosis is sterile vaginal examination with a speculum to identify clear fluid leaking from the cervix or pooling in the posterior fornix. Use nitrazine paper to assess the fluid collected from the posterior fornix for alkaline pH; this method has a positive predictive value (PPV) of 99% and negative predictive value (NPV) of 96%.1 The appearance of “ferning”—a crystalline pattern that occurs when the saline amniotic fluid dries—carries a PPV of 98% to 99% and a NPV of 90% to 99%.2
One must also consider the patient’s history. When that history and the physical exam fail to render a clear result, use US to assess the amniotic fluid volume. A low volume in the presence of a convincing clinical history is very suspicious for PROM, as in the case just described.
Tinting the amniotic fluid may help
In equivocal cases, mix 1 to 3 mL of indigo carmine with 5 mL of sterile saline and insert it into the amniotic fluid under US guidance. This dye will make any leaking amniotic fluid obvious. Be aware, however, that instillation of the dye is very difficult in cases of severe oligohydramnios or anhydramnios. In this setting, amniocentesis can also cause contractions or vaginal bleeding.
New diagnostic tool on the horizon
Recent studies have focused on a new rapid test (AmniSure) that uses immunochromatography to detect trace amounts of placental α-microglobulin-1 protein.3 This protein is specific to amniotic fluid and present in vaginal secretions only when amniotic fluid is leaking through the cervix. One study of 203 patients suspected of having ruptured membranes found the AmniSure test to have a PPV of 100% and NPV of 99.1%.3 Although these findings are promising, further confirmatory studies are needed before this product can be recommended for widespread use.
CASE continued: Leakage of tinted fluid confirms PROM
Because the diagnostic steps taken so far have been inconclusive, J.S. undergoes amniocentesis with infusion of indigo carmine. Within 2 hours, blue dye is observed leaking from the cervix, confirming PROM. A sample of amniotic fluid obtained at the time of amniocentesis produces a negative gram stain and reveals a normal glucose level and leukocyte count. Amniotic fluid cultures are pending.
What is your next step?
Determining the best management strategy is next. The treatment plan should be based on gestational age, presence or absence of infection or labor, and fetal status. Therefore, the initial evaluation of a patient with PROM should focus on the collection of this clinical information.
I recommend these measures:
- Document the exact gestational age by careful review of available records and ultrasound biometry
- Identify indicators of infection, such as maternal fever and tachycardia, fundal tenderness, fetal tachycardia, and an elevated white blood cell count
- Amniocentesis may be required to rule out amnionitis in cases where the diagnosis is clinically unclear
- Document fetal presentation
- Initiate fetal heart rate (FHR) monitoring at the time of diagnosis and perform a biophysical profile (BPP).