Use of beta subunit of human chorionic gonadotropin assay as a diagnostic tool for prelabor rupture of membranes.

PURPOSE: The study aimed at assessment of the accuracy of the β-hCG test in vaginal washing fluid for diagnosis of prelabor rupture of membranes (PROM).

PATIENTS AND METHODS: Two groups of pregnant women from 17 to 38 weeks of gestation were recruited. The first group (PROM group) included 50 pregnant women with unequivocal PROM. The other group included 50 pregnant women with intact membranes. A sterile speculum examination was performed. If less than 5 cc was collected or no fluid found, 10 cc sterile saline was sprinkled on the vaginal wall and 5 cc were recollected in a sterile syringe. Two drops of collected fluid were used for qualitative testing of β-hCG. The remaining fluid was used for quantitative assessment of β-hCG.

RESULTS: The quantitative β-hCG test results were significantly higher in PROM group (median and range: 138.5 (23-475) versus 13 (1-55); the difference in medians and 95% CI: 105 (91-166); p value: <.001). The qualitative β-hCG test was positive in 42/50 (84%) of the PROM group, while it was negative in 50/50 (100%) of the intact membranes group. Areas under receiver operating characteristics (AUC) for both the quantitative and qualitative β-hCG tests were high (0.97, 95% CI: 0.91-0.99, p value: <.001 and .92, 95% CI: 0.84-0.96, p value: <.001, respectively). The suggested cut-off of β-hCG for the quantitative test was 32 mIU/ml. The sensitivity of quantitative and qualitative tests are: 94, 95% CI: 83.5-98.7% and 84, 95% CI: 70.9-92.8%, respectively. The specificity of quantitative and qualitative tests are: 94, 95% CI: 83.5-98.7% and 100, 95% CI: 92.9-100%, respectively.

CONCLUSION: β-hCG test (either quantitative or qualitative) in vaginal washing fluid can be used in the diagnosis of PROM in both preterm and term cases.