Dr Ladan Haghighi, Department of Obstetrics and Gynecology, Shahid Akbar-abadi Maternity Hospital, Mowlavi St, Tehran 1168743514, Iran. Email: firstname.lastname@example.org
Aim: The aim of this study was to evaluate the reliability of vaginal fluid creatinine for the diagnosis of premature rupture of membranes (PROM).
Material and Methods: A total of 180 pregnant women were enrolled in the study. Group I (confirmed group) consisted of 60 women with a diagnosis of rupture of membranes confirmed by visualization of fluid passing from the cervical canal. Group II (suspected group) consisted of 60 women with a complaint of vaginal fluid leakage but without obvious amniotic fluid flowing from the cervix or vaginal pooling with negative nitrazine test. The control group (group III) consisted of 60 women without any complaint or complication. All patients were sampled for vaginal fluid creatinine by speculum examination. One-way ANOVA, χ2, and Kruskal-Wallis test, as well as receiver operating characteristic (ROC) curve analysis were used.
Results: The mean vaginal fluid creatinine in groups I, II, and III were 1.74 ± 0.8, 0.45 ± 0.2 and 0.25 ± 0.1 mg/dL, respectively. The creatinine level was significantly higher in the confirmed group (group I) than in the other two groups (P < 0.0010). The optimal cut-off value was 0.5 mg/dL with 96.7% sensitivity, 100% specificity, 100% positive predictive value, and 96.8% negative predictive value.
Conclusion: Vaginal fluid creatinine determination for the diagnosis of PROM is reliable, simple, rapid and inexpensive.
Premature rupture of membranes (PROM) occurs in 10% of all pregnancies and is a major cause of preterm birth and perinatal morbidity and mortality.1 Correct diagnosis of PROM is crucial for appropriate management and requires a judicious assessment of history, clinical findings and specialized tests. Failure to identify patients or false-positive diagnosis of membrane rupture may lead to inappropriate management and serious maternal/neonatal complications or unnecessary obstetric interventions. The diagnostic tests currently used in clinically asymptomatic or suspicious cases include measurement of vaginal pH, alpha fetoprotein (AFP), human chorionic gonadotropin (hCG), diamine oxidase, prolactin, insulin growth factor binding protein-1 (IGFBP-1), fetal fibronectin and fern test. However, none of these tests diagnose or exclude rupture of membranes (ROM) with certainty.2–6 Knowing that fetal urine is the most important source of amniotic fluid in the third trimester, in recent years some studies have suggested measurement of creatinine in vaginal fluid for the diagnosis of ROM.7–9 The present study evaluates the reliability of creatinine measurement for the diagnosis of ROM.
Material and Methods
One hundred and ninety-three pregnant women with a singleton pregnancy and gestational age (GA) of 28–40 weeks who were admitted to Shahid Akbar-abadi teaching hospital were recruited into this observational study. The study was approved by the ethics committee of Tehran University of Medical Sciences. The study group consisted of 133 pregnant women with a complaint of vaginal fluid leakage (case group) and 60 normal pregnant women admitted to the prenatal clinic for regular prenatal control visits with no complaints or complications and who were selected randomly (control group).
Thirteen women in the first group were excluded from the study due to the presence of vaginal spotting/ bleeding, uterine contractions or medical/prenatal complications. GA was determined according to the sonography of the first half of pregnancy. All women in the first group underwent a sterile speculum examination to confirm amniotic fluid (AF) flowing from the cervix. Positive results were considered as ‘confirmed PROM group’ (group I), while patients with a complaint of vaginal fluid leakage and no obvious AF flowing or AF pooling with negative nitrazine test were considered as ‘suspected PROM group’ (group II). There were 60 participants in each group. All women underwent sonographic examination for determination of AF and GA.
In cases of flowing/pooling AF, for creatinine sampling, vaginal fluid aspiration after injection of 3 mL of sterile water into the posterior vaginal fornix with the same syringe was performed, while in the control group, initially 5 mL of sterile water was injected into the posterior vaginal fornix; thereafter, 3 mL was aspirated with the same syringe. Samples were immediately sent to the Shahid Akbar-abadi Teaching Hospital laboratory, centrifuged and kept refrigerated at −30°C. All speculum examinations, sample collections, and sonographic examinations were performed by the same physician. Age, parity, GA, and creatinine level were compared using one-way ANNOVA and χ2 test, while dilatation and effacement were compared using Kruskal-Wallis test. Receiver operating characteristic (ROC) curve analysis was used to establish an optimal cut-off point. The significance level was set at 0.05.
Demographic data, clinical characteristics and vaginal fluid creatinine level in all three groups are shown in Table 1. The three groups were similar with respect to maternal age, parity, gestational age, dilatation, effacement, and amniotic fluid index. The mean vaginal fluid creatinine concentration in group I was higher than the other two groups (post hoc test).
Table 1. Demographic data, clinical characteristics and vaginal creatinine levels of three groups of patients
Maternal age (year ± SD)
26.7 ± 4.7
4.4 ± 26.1
4.3 ± 25.9
2.85 ± 1.05
1.1 ± 2.71
1 ± 2.93
Gestational age (w)
36.5 ± 3.5
37.5 ± 2.2
36.9 ± 2.3
Amniotic fluid index (mm)
81.1 ± 30.2
89.2 ± 34.05
95 ± 28.1
Vaginal fluid creatinine (mg/dL)
1.74 ± 0.8
0.45 ± 0.2
0.25 ± 0.1
Cervical dilatation (cm)
1.53 ± 0.21
1.48 ± 0.8
1.61 ± o.25
Cervical effacement (%)
27 ± 3
31 ± 4.5
28 ± 4
The ROC curve analysis was used to determine the optimal cut-off value (Fig. 1). Sensitivity, specificity, positive predictability, and negative predictability in different cut-off values are represented in Table 2.
Table 2. Vaginal fluid creatinine level (mg/dL)
Positive predictive value
Negative predictive value
The sensitivity (96.5%), specificity (100%), positive predictive value (PPV) (100%), and negative predictive value (NPV) (96.8%) were highest in detecting PROM by evaluation of vaginal fluid creatinine concentration with a cut-off value of 0.5 mg/dL.
Correct and timely diagnosis of PROM is essential for optimizing pregnancy outcome, and management is based on accurate diagnosis. Still, a non-invasive diagnostic gold standard is not available and the traditional non-invasive diagnostic methods, including pooling assessment, microscopic fern test, and pH examination of cervicovaginal discharge (nitrazine test), have limitations in terms of cost, simplicity, and diagnostic accuracy, especially with passage of time since membrane rupture. However, the gold standard for diagnosis of PROM, amnio-dye test, is invasive and carries risks of infection, abruption, and abortion.7
In recent years, researchers have focused on detecting various biochemical markers in cervicovaginal discharge when ROM occurs. These markers include AFP, fetal fibronectin, IGFBP-1, prolactin, β-hCG, urea, lactate, placental alpha-microglobulin-1 and 2, and creatinine.9
This is the fourth study to use vaginal fluid creatinine determination for the diagnosis of PROM. Li HY et al.7 found that measurement of creatinine in vaginal fluid is cheaper and easier than hCG. In another study Gurbuz et al.8 reported that measurement of vaginal fluid creatinine with a cut-off value of 0.12 mg/dL and sensitivity, specificity, NPV and PPV of 100% in detecting PROM, is cheaper and faster than other methods.
Kafali et al.9 reported that determination of urea or creatinine in vaginal fluid for the diagnosis of PROM is a reliable, simple and rapid test with sensitivity, specificity, NPV and PPV of 100% with a cut-off value of 12 and 0.6 mg/dL, respectively. They speculated that analysis of vaginal creatinine and urea can be used as fetal maturation test in cases of preterm labor as creatinine level of AF depends on gestational ages. The results of the present study, similar to those by Kafali et al. show that evaluation of vaginal fluid creatinine concentration with 96.5% sensitivity, 100% specificity, 100% PPV and 96.8% NPV with a cut-off value of 0.5 mg/dL is a valid and simple test, especially considering that it costs much less than hospitalization or other tests, such as placental alpha-macroglobulin-1 with similar sensitivity and specificity ($5 vs $60 dollars for every patient) in suspicious cases.