PROM is an important obstetric event that tends to occur in approximately 8 – 10% of all pregnancies and it is associated with maternal and neonatal complications. These complications include infections, preterm labor, and neonatal respiratory distress syndrome [1]. The perinatal outcomes in such conditions depend on the accurate and timely diagnosis and appropriate prediction of labor onset. Several traditional methods have been used for diagnosing PROM including the use of atrazine test, fern test, and pooling of amniotic fluid. These methods have limitations in sensitivity and specificity, especially in cases where the rupture is minimal [2]. There has been interest in finding some biochemical markers that are accurate which included fetal fibronectin, insulin-like growth factor-binding protein-1 (IGFBP-1), and placental alpha microglobulin-1 (PAMG-1) [3]. Among these biochemical factors, vaginal fluid lactate measurement has evoked interest because it is a promising, non-invasive marker with potential for diagnostic and prognostic implications in cases of PROM. The amount of lactate in vaginal secretions serves as a sign of cellular stress and hypoxic conditions along with inflammatory responses which frequently appear at PROM or the start of labor. Researchers base their assessment of when preterm labor will start on measuring lactate within vaginal fluids because they have documented that increased lactate accompanies heightened myometrial activity together with inflammatory processes that increase the risk of uterine contractions [4]. Measuring lactate levels has potential as a natural biological indicator for labor initiation among women with premature rupture of membranes. Since the timing of labor onset following PROM is important for decision making, in term pregnancies most women go into labor spontaneously within 24 hours of rupture of membrane. However, in a few cases, there could be a delayed onset of labor which increases the risk of ascending infections such as chorioamnionitis and endometritis (5). On the contrary unnecessary early induction could lead to increased cesarean delivery and other interventions. Therefore, identifying patients who are likely to go into spontaneous labor in a short time could help in reducing unnecessary interventions.

Few studies have explored the association between elevated vaginal lactate levels and the onset of labor, and have found potential utility in clinical decision-making [6]. However, its utility as a prognostic marker for the timing of spontaneous labor onset in confirmed cases of PROM remains an area of research interest. Based on this background the present study was designed to assess the association between vaginal fluid lactate levels with the timing of spontaneous onset of labour in women with suspected pre-labour rupture of membranes. The results of this study could aid clinicians in optimizing timing for interventions and improving maternal-fetal outcomes.  Given this background, the present study aims to assess the association between vaginal fluid lactate levels and the timing of spontaneous onset of labor in women with suspected pre-labor rupture of membranes. Establishing this association could potentially aid clinicians in optimizing timing for interventions and improving maternal-fetal outcomes.

This was a hospital-based, observational cross-sectional study conducted in the Department of Obstetrics and Gynaecology in coordination with the Department of Biochemistry at a tertiary care center. The study was conducted over a defined period after obtaining approval from the Institutional Ethics Committee. Written informed consent was obtained from all study participants after explaining the nature of the study in a vernacular language.

Participants: The study cohort consisted of 88 pregnant women presenting with singleton pregnancies beyond 34 completed weeks of gestation and a clinical suspicion of prelabour rupture of membranes (PROM). Eligibility was determined based on inclusion and exclusion criteria.

Inclusion Criteria:

1. Pregnant women with gestational age >34 weeks,
2. singleton pregnancy in cephalic presentation,
3. And no signs of active labor.

Exclusion Criteria:

1. Women with multiple gestations,
2. known congenital fetal anomalies,
3. gestational diabetes,
4. hypertensive disorders of pregnancy,
5. meconium-stained liquor, clinical signs of chorioamnionitis,
6. Any medical or obstetric complications requiring immediate intervention.

Variables and Grouping Participants were divided into two groups based on findings of sterile speculum examination:

• Group 1 (Visible): Women with visible pooling of amniotic fluid in the posterior vaginal fornix (n = 40).
• Group 2 (Non-visible): Women with no visible fluid seen on speculum examination (n = 48).

A total of 98 participants were included based on availability during the study period and assuming adequate statistical power to detect significant differences in vaginal lactate levels between the two groups. To reduce selection bias, only women fulfilling clear inclusion criteria and presenting within a similar time window after suspected PROM were enrolled. Confounding variables such as gestational age and parity were accounted for during the analysis. The primary variable of interest was vaginal fluid lactate concentration measured at the time of examination. The main outcome was the timing of the spontaneous onset of labor, defined as the occurrence of regular uterine contractions associated with progressive cervical dilation within 24 hours of presentation.

Data Sources and Measurement:

Clinical and demographic details such as maternal age, parity, gestational age at presentation, and time since suspected membrane rupture were also collected using a structured proforma. All the women in the study had undergone sterile speculum examination and 50 microlitres of vaginal fluid were collected in a micro pipette for analysis of lactate levels. Lactate levels were analyzed by the kinetic method in the Auto analyzer using a spin react kit. The levels were determined within 2-3 hours and if not possible, the sample was stored at -200C and the lactate levels were determined within 24- 48 hours. These patients were followed up for the spontaneous onset of the active phase of labor, which is defined as regular painful contractions of more than 3 in number lasting for 40 to 45 seconds within 10 minutes with cervical dilatation of 4 centimeters.

Statistical Analysis:

Data was segregated, refined, and uploaded to an MS Excel spreadsheet and analyzed using SPSS software (version 23 in Windows format). Continuous variables were expressed as mean ± standard deviation and compared using the independent t-test or Mann-Whitney U test as appropriate. Categorical variables were compared using the Chi-square test or Fisher’s exact test. A p-value of <0.05 was considered statistically significant.

The baseline characteristics of the study cohort presented in Table 1, demonstrate that 98 participants had amniotic fluid pooling visible (Group 1 n=40) while 48 participants exhibited no visible pooling (Group 2). The patient groups demonstrated similar values for maternal age (26.4 ± 3.8 vs. 27.1 ± 4.2 years, p=0.412) and gestational age (37.2 ± 1.5 vs. 36.9 ± 1.7 weeks, p=0.387) together with BMI (24.1 ± 2.3 vs. 23.8 ± 2.1 kg/m², p=0.527). Although Group 2 had more nulliparous women compared to Group 1 (62.5% vs. 55%), the difference did not reach statistical significance (p=0.215). Women in both groups underwent PROM procedures that lasted a comparable period of 5.2 ± 2.1 hours and 4.8 ± 1.9 hours (p=0.341).

Table 2 shows the vaginal fluid lactate levels in the cohort of the study. Group I has significantly higher lactate levels had mean levels of 10.2 ± 2.4 mmol/L and a median of 9.8 mmol/L (IQR: 8.1–11.7). The range was from 6.5 – 15.2 mmol/L. In comparison the group 2 cases had a mean lactate level of 6.3± 1.9 mmol/L the median value was 6.1 mmol/L (IQR: 5.2–7.5) and the range of 3.8 to 10.1 mmol/L. The analysis shows that the p values was (<0.001) which shows that there was a significant difference between the values between the two groups. This shows that group I had higher chances of spontaneous labor onset compared to group 2.

                              *Significant

Table 3 depicts the association between the visible pooling of amniotic fluid and the onset of spontaneous labor in 24 hours. A critical analysis of the table shows that in Group 1, cases 85% (34/40) of participants experienced labor onset within 24 hours. Whereas in Group 2 the onset of labor was found in only 45.8% (22/48). The relative risk of labor onset in group 1 was found to be .86 (95% CI: 1.32–2.61). This shows that the women in visible pooling were nearly twice as likely to go into spontaneous labor in 24 hours. This difference was statistically significant (p < 0.001), highlighting a strong association between visible amniotic fluid pooling and imminent labor onset in cases of suspected pre-labor rupture of membranes.

                           *Significant

Table 4 of the study shows the predictive accuracy of vaginal fluid lactate levels for the onset of spontaneous labor. We found that the lactate cutoff values of ≥8.5 mmol/L show high sensitivity (82.1%) and specificity (84.4%), with a positive predictive value (PPV) of 88.6% and a negative predictive value (NPV) of 76.3%. The area under the curve values was 0.89 (95% CI: 0.82–0.95). This shows that it has excellent diagnostic performance. However, at the lower cut-off of ≥7.0 mmol/L, sensitivity increased to 92.9%, but specificity dropped to 68.8%. The positive predictive value was 81.3% and the negative predictive value was 87.5%. The area under the curve was 0.81 (95% CI: 0.73–0.89). Since the area of the curve at the cutoff of ≥8.5 mmol/L has a greater area, it is a better indicator of spontaneous labor onset. The p values were found to be (<0.001) which indicates it is significant.

Table 5 shows the results from a multivariate logistic regression model to determine the independent factors related to spontaneous labor onset in the cohort of this study. Spontaneous labor was five times more likely in cases where lactate levels were ≥8.5 mmol/L (OR 5.2, 95% CI: 2.1–12.8, p=0.001). Visible pooling of amniotic fluid proved to be a meaningful predictor of labor since the adjusted OR reached 3.8 (95% CI: 1.5–9.6, p=0.005). The statistical analysis identified that nulliparity (OR: 1.2, p=0.624) and gestational age (OR: 1.1, p=0.312) failed to demonstrate statistically significant relationships with spontaneous labor onset. Elevated lactate levels combined with visible fluid pooling stand as independent indicators that point toward the rapid onset of labor during suspected pre-labor rupture of membranes.

                                        *Significant

This ROC curve (Figure 1) of our study shows the diagnostic performance of lactate levels at two cutoff thresholds (≥7.0 mmol/L and ≥8.5 mmol/L) for predicting spontaneous labor onset. This curve shows that there is improved specificity at a higher cutoff value of ≥8.5 mmol/L by shifting leftwards and still maintaining strong sensitivity. The AUC performance of both cutoff values is (0.81 for ≥7.0 and 0.89 for ≥8.5) showing good overall predictive ability. Since 8.5 mmol/L threshold achieves a good balance of true positive and false positive rates. This shows its clinical utility in predicting women at risk of imminent labor onset in suspected pre-labor rupture of membranes.

The current study was done to investigate the association between vaginal fluid lactate levels and the timing of spontaneous labor onset in women with PROM. The study included 88 women with PROM divided into two groups based on visible pooling of amniotic fluid. The comparison of baseline characteristics (Table 1) shows that both groups were comparable in all characteristics. Our findings demonstrate strong internal validity because the participant sample possesses similar characteristics which improve our ability to trace labor onset variation to lactate levels and visible pooling.  We found that vaginal fluid lactate levels were significantly higher in Group 1 compared to Group 2 (mean 10.2 vs. 6.3 mmol/L, p < 0.001). The spontaneous labor onset occurred within 24 hours in 85% of Group 1 versus 45.8% in Group 2 (RR 1.86, p < 0.001). The estimation of cutoff of lactate levels ≥8.5 mmol/L showed strong predictive accuracy (AUC 0.89). The logistic regression analysis confirmed that lactate levels and visible pooling as independent predictors of spontaneous labor onset.

The analysis of Group 1 cases with visible amniotic fluid pooling, had significantly higher vaginal fluid lactate levels (mean: 10.2 ± 2.4 mmol/L) compared to Group 2 non-visible group (mean: 6.3 ± 1.9 mmol/L, p<0.001). The elevated lactate levels are attributable to increased anaerobic metabolism of fetal membranes or cervicovaginal tissues preceding labor onset, as previously suggested by other studies [7, 8] This supports the hypothesis that vaginal fluid lactate could serve as a non-invasive biomarker for imminent labor onset. In our study 85% of women in Group I showed spontaneous onset of labor as compared to 45.8% of Group 2 (p<0.001) with a relative risk of 1.86 (95% CI: 1.32–2.61). This is in agreement with the observation of previous studies showing that visible pooling is one of the clinical predictors of labor progression in PROM cases. [9-11] the higher incidence of labor in the visible group could reflect that more advanced cervical or uterine changes are in progression which favors the labor onset.

The diagnostic accuracy of vaginal fluid lactate levels was established by ROC analysis in this study. A cut-off value of vaginal lactate levels of ≥8.5 mmol/L offered high sensitivity (82.1%) and specificity (84.4%) with an AUC of 0.89. This shows that it has excellent predictive performance. In comparison, a lower cut-off value of ≥7.0 mmol/L had increased sensitivity (92.9%) but reduced specificity (68.8%) and a slightly lower AUC of 0.81. Similar findings have been reported by studies of Bohîltea et al. [12] and Kesrouani et al. [13], where they demonstrated that lactate measurement in vaginal secretions can help predict spontaneous labor in PROM cases. The multivariate logistic regression analysis of this study confirmed that ≥8.5 mmol/L was an independent predictor of spontaneous labor (OR 5.2, p=0.001), alongside visible fluid pooling (OR 3.8, p=0.005). On the contrary nulliparity and gestational age did not show significant associations. This shows that the biochemical markers provide superior predictive value compared to traditional clinical parameters [14]. Therefore, it appears that vaginal fluid lactate can be a valuable biomarker for predicting imminent spontaneous labor in cases of suspected PROM, especially when combined with clinical signs of visible vaginal fluid pooling. Future research must be directed to explore its integration into decision-making algorithms for better maternal and neonatal outcomes.

Limitations of this study were smaller sample sizes which could limit the generalizability of findings to broader populations. This was also a single-center study which may cause center-specific biases and decrease external validity. Finally, long-term neonatal outcomes were not evaluated, which would be important for assessing clinical utility.

Within the limitation of the current study, we found that elevated vaginal fluid lactate levels above 8.5 mmol/L, are strongly associated with the onset of spontaneous labor within 24 hours in women with suspected pre-labor rupture of membranes. The visible pooling of amniotic fluid also appears to be significantly correlated with early onset of labor. Therefore, these clinical and biochemical parameters offer valuable predictive utility and could aid clinicians in timely decision-making to optimize maternal and neonatal outcomes. The addition of lactate assessment to clinical protocols enables improved diagnoses and minimizes needless treatments thus establishing itself as an important PROM management tool. Further large-scale studies are warranted for more authentication of the above findings.

1. Mercer BM. Preterm premature rupture of the membranes. Obstet Gynecol. 2003;101(1):178–93.
2. Cousins LM, et al. AmniSure placental alpha microglobulin-1 rapid immunoassay versus standard diagnostic methods for detection of rupture of membranes. Am J Perinatol. 2005;22(6):317–20.
3. Lee SM, et al. The clinical significance of detecting IGFBP-1 and PAMG-1 in patients with suspected rupture of membranes. Am J Obstet Gynecol. 2012;206(1): e1–6.
4. Martius JA, et al. Vaginal fluid lactate as a biochemical marker for the diagnosis of PROM. J Perinat Med. 1996;24(3):243–51.
5. Hannah ME, et al. Induction of labor compared with expectant management for prelabor rupture of the membranes at term. N Engl J Med. 1996;334(16):1005–10.
6. Rutanen EM. Biochemical markers for the detection of premature rupture of membranes. Clin Perinatol. 2001;28(4):661–77.
7. Ratten GJ, Garland SM, Tabrizi SN, Ditchfield M, Chen S, Mitchell CM, et al. Vaginal fluid lactate as a predictor of spontaneous labour. BJOG. 2010;117(8):940–4 6.
8. Borna S, Borna H, Khazardoost S. Vaginal fluid lactate for predicting imminent delivery in women with term premature rupture of membranes. Eur J Obstet Gynecol Reprod Biol. 2014; 176:60–63.
9. Caughey AB, Robinson JN, Norwitz ER. Contemporary diagnosis and management of preterm premature rupture of membranes. Rev Obstet Gynecol. 2008;1(1):11–22.
10. Ekpa QL, Udoudo MI, Nwebeh EI, Nwebeh OC. Preterm Prelabour Rupture of Membrane (PPROM) in a Young Female in South-South Nigeria: A Clinical Case Report. Cureus. 2024 Jan 4;16(1):e51649.
11. Bellussi F, Seidenari A, Juckett L, Di Mascio D, Berghella V. Induction within or after 12 hours of ≥36 weeks' prelabor rupture of membranes: a systematic review and meta-analysis. Am J Obstet Gynecol MFM. 2021 Sep;3(5):100425.
12. Bohîltea R, Turcan N, Cîrstoiu MM, Voicu D, Ionescu C, Tănase F, et al. The relevance of vaginal fluid lactate in predicting the onset of labor. Maedica (Bucur). 2019;14(2):116–21.
13. Kesrouani A, Daya Z, Khalifeh R, Attieh E, Gharios J, Haddad D, et al. The use of lactate in vaginal secretions to predict the risk of preterm labor. J Matern Fetal Neonatal Med. 2021;34(8):1309–14.
14. Smith R. Parturition. N Engl J Med. 2007;356(3):271–83.