Impact of Complete Blood Count (CBC) Parameters in Preterm Birth Prediction in Cases with Threatened Preterm Labour (TPL)

Background : Preterm birth is one of the main causes of neonatal morbidity and mortality in pregnancies worldwide. This investigation is undertaken to determine the usefulness of neutrophil-to-lymphocyte ratio (NLR) and platelet-to-lymphocyte ratio (PLR), which are complete blood count (CBC) parameters, in predicting preterm birth among women with threatened preterm labour (TPL). Methods : A retrospective observational study was conducted between 2019 and 2023, and medical charts of 250 pregnant patients internalized for TPL were investigated. A hundred and forty of them gave birth prematurely, and remaining 110 women who responded to bed rest and medical treatment constituted the control group. NLR, PLR and other inflammatory markers such as systemic immune-inflammation index (SII = neutrophil × platelet/lymphocyte count) were recorded, and their probable correlations with preterm delivery were evaluated. Logistic regression and area under curve (AUC) analysis were used to assess the predictive value of these markers. Results : There were no significant differences between those who delivered at term and patients with preterm labour who delivered < 37 weeks according to demographic data and gestational history. However, there were notable discrepancies when considering certain clinical and laboratory findings, such as cervical length (CL), SII, and NLR. CL had a strong relationship with the risk of preterm delivery (odds ratio (OR) = 0.95, 95% confidence interval (CI) = 0.92–0.98, p = 0.001). SII and NLR values were seen to be higher in patients with preterm labour compared with control group, indicating a rise in inflammatory activity (1489.4 ± 1113.3 vs . 1043.9 ± 587.1, respectively, p = 0.001 for SII; and 5.6 ± 3.4 vs . 4.8 ± 3.0, respectively, p = 0.02 for NLR). However, NLR had a low predictive power with an AUC of 0.581. Conclusions : SII seems to have an important predictive value for preterm delivery, similar to CL measurements already used in the clinic. Even patients with preterm delivery had higher NLR, clinical interpretation of AUC value reduces its predictive power. Therefore, further research is needed to refine our results and to advance its use in clinical practice.


Introduction
The appearance of preterm birth continues to be an important issue in public health among women of reproductive age, because it is the leading cause of perinatal morbidity and mortality worldwide [1,2].Wide range of its etiological factors, from congenital fetal malformations, insufficient intrauterine growth or macrosomia to maternal diabetes mellitus (DM), hypertension (HT) or other chronic disorders induced by the inflammation, makes it difficult to accurately determine the definitive cause [3][4][5].Therefore, this medical condition creates an unclear area in its prediction and in planning early intervention.
Since almost half of all premature deliveries have no apparent risk factors and most of the current methods do not have enough sensitivity or specificity in the prediction of preterm births, new easily applicable tests or predictive models are needed to reduce unnecessary medical interventions and to prevent its negative consequences [6].Therefore, our study is based on a main hypothesis that some parameters of complete blood count (CBC), such as neutrophil to lymphocyte ratio (NLR) together with platelet to lympho-cyte ratio (PLR), can work as reliable indicators that show whether labour will occur before the expected time.To support this idea, further secondary hypotheses were postulated considering that these figures may indicate underlying inflammatory processes which are known to be induced by premature labour [7][8][9][10][11].
As a consequence, the present study is designed to determine the probable predictive values of NLR and PLR in relation to the chances in early labour among women who present with signs or symptoms of threatened preterm labour (TPL).

Materials and Methods
After the approval of study by institutional review board of University of Health Sciences Turkey, Istanbul Education and Research Hospital (date: 13.10.2023/number:269), medical records of patients who were admitted with a diagnosis of TPL between January 2019 and October 2023 were reviewed.Patients signed written informed consent allowing their data to be used in medical researches.Study was carried out in accordance with the declaration of Helsinki.The objective was to evaluate the predictive value of the parameters of CBC and inflammatory markers for TPL among pregnant women with symptoms suggesting this condition.Medical charts of 250 pregnant patients internalized for TPL were investigated.A hundred and forty of them gave birth prematurely (preterm labour group), and remaining 110 women who responded to bed rest and medical treatment (term labour) constituted the control group.

Inclusion Criteria
TPL was defined as the progression of cervical dilatation and ripening caused by regular uterine contractions occurring before 37 weeks of pregnancy, which may result in preterm birth [12].To be included in the present study, all admitted patients with TPL should fall within the age range of 18-48 years, and their diagnosis should have been made in our institution where synchronised CBCs were performed during treatment and at birth.

Exclusion Criteria
If any patient did not meet these conditions, such as twin pregnancy and being too young or too old, they were considered to be ineligible to enrol in the study.Also excluded were cases where gestation exceeded 37 weeks or an early membrane rupture occurred before admission followed by vaginal bleeding, placenta previa, oligohydramnios, or placental abruption.Patients with missing information in their files and those with any documented infectious or inflammatory disorders were also excluded.

Treatment Protocol
All participants received treatment according to standard clinical protocols for the management of preterm labour [13,14].This involved a strict bed rest and administration of corticosteroids, tocolytics and antibiotics.

Data Procurement and Variables
The variables analysed included age, gestational history, risk factors for preterm labour such as gestational diabetes or higher serum glycosylated hemoglobin levels, obesity or higher body mass index (BMI) and smoking history.Cervical length (CL), hemogram findings and inflammatory markers such as systemic immune-inflammation index (SII), NLR, PLR and monocyte to lymphocyte ratio (MLR) were recorded at the beginning of labour.NLR was calculated as the absolute neutrophil count divided by the absolute lymphocyte count, and PLR was calculated as the absolute platelet count divided by the absolute lymphocyte count.SII was defined as [neutrophil count × platelet count/lymphocyte count].All data were recorded at Excel programme (Microsoft 2017, Chicago, IL, USA).AP-GAR (appearance, pulse, grimace, activity and respiration) scores of newborns were recorded at 1 minute and 5 minutes after birth [15].

Statistical Analysis
Statistical package for social sciences (SPSS version 11.5, Chicago, IL, USA) was used for the statistical analysis.Descriptive statistics such as mean, standard deviation (SD), median, and interquartile range were applied to the data.Shapiro-Wilk normality test was used to check whether they follow normal distribution or not.The independent t-test was done to compare groups of variables having a normal distribution, while the Mann-Whitney U test was used to compare those without a normal distribution.The Chi-square test was also employed to compare qualitative data.Logistic regression analysis helped identify factors associated with delivery before 37 weeks, and receiver operating characteristic (ROC) curves were used to determine the diagnostic precision of the markers.All results were considered statistically significant at p value < 0.05.

Results
A total of 140 expectant mothers gave birth before 37 weeks during this period (preterm labour group), and pregnant women who gave birth at term (>37 weeks) were used as control group (n = 110).Demographic and gestational variables including age (27 ± 6 vs. 26.4± 5.7 years in preterm labour and control groups, respectively, p > 0.05), gravida, parity and abortion were similar in both groups (each, p > 0.05, Table 1).Risk factors for preterm labour such as higher BMI or glycosylated hemoglobin and smoking were not significantly different, as well (Table 1).However, CL was significantly shorter in the preterm group than in the term (control) group (23.2 ± 10.0 vs. 28 ± 7.9 mm, respectively, p = 0.001, Table 1), indicating its predictive value for preterm delivery.There was no important complication during deliveries in both groups.On the other hand, APGAR score was found to be significantly different between the groups, and lower values were recorded among babies born too early than those born at full term (7.4 ± 0.9 vs. 7.8 ± 0.5 at 1 minute and 8.1 ± 0.8 vs. 8.6 ± 0.5 at 5 minutes, respectively; both, p = 0.001, Table 1).
Most of the CBC parameters, such as white blood cells, hemoglobin, hematocrit, red cell distribution width (RDW) and platelet distribution width (PDW), were similar between two groups (each, p > 0.05, Table 2).In addition, counts of neutrophils, monocytes and lymphocytes in both groups were also non-significant (each, p > 0.05).However, platelet count of the preterm group was higher than that of the term group (253.6 ± 72.9 vs. 232.5 ± 53.4 × 10 9 /L, respectively, p = 0.01).Similarly, PLR was higher in preterm labour group (151.2 ± 87.9) in comparison with the control group (135 ± 74); even the difference was not statistically significant (p = 0.12).
ROC curves were depicted to test the performance of diagnostic markers in correctly identifying positives and negatives as its threshold is varied.The area under the curve (AUC) measures the separability achieved by the model: an AUC near 1 indicates excellent performance; approximately 0.5 suggests that there is no ability to discriminate between different groups based on any variables.In our study, CL was identified as the most powerful predictor of preterm delivery, where the odds ratio (OR) for a decrease in risk per mm = 0.95 (95% confidence interval (CI) = 0.92-0.98,p = 0.001, Table 3).NLR and SII had moderate predictive value in our setup study, (more for SII than for NLR), since SII showed better performance in terms of AUC with cut-off >1568.5 leading to a sensitivity of approximately 39% and specificity above 89% (p = 0.02, Tables 3,4,5, Fig. 1).On the other hand, NLR was also a promising marker at cut-off level >4.7, with 50% sensitivity and 69% specificity (AUC 0.581, Tables 3,4,5, Fig. 1).However, NLR had a low predictive power with this AUC value.Therefore, even patients with preterm delivery had higher NLR, clinical interpretation of AUC value was seen to reduce its predictive power.

Discussion
Although many factors are blamed for the aetiology of preterm births, one of the main ones is inflammation and its related processes [5,9,10].Complex causality and restricted predictive markers make the diagnosis of preterm delivery difficult.This complex problem has considerable implications for health and quality of life, as premature babies are more likely to have serious health problems that can translate into long-term developmental disabilities [3,4].Furthermore, the economic burden on families and healthcare systems requires further investigation of these predictors.Such an investigation might be able to reduce such burdens through predictions that can be acted upon.Therefore, it is necessary to determine different inflammatory profiles among pregnant women using indicators, such as NLR or PLR, so that interventions against risks associated with premature labour could be better individualised [11,16,17].In this sense, the current study adds weight to the need for improved tools to predict early intervention strategies through new biomarkers.
Several recent investigations have associated some markers of inflammation with adverse pregnancy outcomes [16][17][18][19].Even there are conflicting results, in some of these studies, increased levels of NLR and/or PLR can imply a generalised inflammatory response which is a risk factor for preterm delivery [9,11,18,19].Such indicators are useful in clinical settings where rapid non-invasive diagnostic tests should be applied to assess the risk of symptomatic pregnant women toward preterm labour.Gestational diabetes, cigarette smoking and obesity are well-known risk factors and the main predictors of premature labour [3,20].However, in most of the cases, the patient does not have any of these risk factors, and CL is the only diagnostic test or follow-up tool to save time in taking precautions to prevent labour from progressing [21,22].Similarly, our research shows that it is very difficult to predict or control preterm labour through a detailed interrogation of risk factors, demographic features, gestational history or routine laboratory tests, except the serial measurements of CL.
Many recent studies have found that shorter cervix increases the risk of giving birth too soon among women at high risk for this condition [23,24].There are also other studies suggesting that systemic inflammation can lead to early uterine contractions resulting in premature births [25].Furthermore, a current study on spontaneous preterm birth phenotyping has defined immune-mediated factors as the main factor potentially leading to initiation of delivery [26].On the other hand, traditional definition of TPL based on gestational age alone makes it necessary to offer a new taxonomy including maternal, placental, and fetal conditions routinely recorded in data collection systems [27].
Our findings support the primary and secondary hypotheses of the present study that inflammatory processes could play a role in the induction of preterm birth indicated by a shorter CL together with elevated systemic markers SII and NLR.We observed that there was a strong association with each millimeter reduction in CL and preterm delivery according to our logistic regression and ROC analyses.Therefore, local environment can be affected by widespread inflammation, and may lead to premature labour by shortening CL.The predictive value of SII was more significant, since increase in NLR was accompanied with a narrow ROC curve indicated by a borderline AUC value.On the other hand, it has already been demonstrated that systemic inflammation can also cause direct uterine contractions.These results imply that we need multiple approaches involving both traditional methods and new markers if we want better assessment tools to identify those at risk of going into early labour and to take preventive measures.
The present study has several strengths.It has a comparably large sample size and provides information on diagnostic tests and follow-up practices in such a specific population.This enhances external validity, i.e. the generalisability of the method.On the other hand, main limitations of the study are its retrospective design and observational nature leaving the possibility of confounding bias.

Conclusions
It is very difficult to predict preterm labour, and an all-inclusive approach seems to be logical and necessary.Therefore, traditional clinical assessments can be combined with new biomarkers so that predictions can become more precise and management strategies better to deal with this problem.SII seems to have an important predictive value for preterm delivery, similar to CL measurements already used in the clinic.On the other hand, even patients with preterm delivery had higher NLR, clinical interpretation of AUC value reduces its predictive power.Therefore, further research is needed to refine our results and to advance its use in clinical practice.