Role of maternal serum c-reactive protein levels in early second trimester as a marker of preterm labour: A study protocol

Introduction

Labor is a physiological process during which fetus and viable products of conception are expelled through the vagina into the world. Labor typically starts for most women between 37 and 42 weeks of pregnancy. Preterm or premature labour is defined as beginning before 37 weeks of pregnancy.¹ In developing nations, preterm labour is the main contributor to prenatal morbidity and mortality. Preterm birth rates vary by country and range from 5% to 18% of all births.²

However, despite decades of research, little progress has been achieved in determining its cause, physiology, and aetiology. There are high chances of cerebral impairment, respiratory distress, feeding, visual, and hearing difficulty for newborns who survive.

The most frequent cause of preterm labour, which accounts for about 50% of premature birth is idiopathic. Up to 40% of women who give birth prematurely through spontaneous labour lack obvious, well-known risk markers for preterm labour. 18.7% to 28.8% of preterm births are caused by iatrogenic (medical) causes related to maternal or fetal factors like hypertensive disease, gestational diabetes and twin pregnancies or intrauterine growth restriction respectively. Of all preterm births, early rupture of the membranes occurs in 7.1% to 51.2% (or 25% on average) of cases.³ Identification of those at risk is a crucial first step in combating the issue of preterm birth. Risk score systems, biochemical markers of inflammation, and infection screening are some of the methods that have been considered. In the asymptomatic population, it is crucial to assess these possible predictors both singly and together, as well as to consider the financial implications of these screening procedures. Numerous studies have identified a link between inflammation or infection and premature birth. Although there is evidence that bacterial vaginosis increases the risk of preterm birth, antibiotic treatment has not been proven to offer any protective advantages. In order to identify infection in pregnant women who experienced premature membrane rupture and preterm labour, maternal concentrations of CRP have been examined. Few studies have found an association between maternal blood CRP levels that are elevated in the second trimester and subsequent preterm birth. The current study's objective is to assess maternal serum CRP.

Protocol

Methods

The institutional ethical committee's ethical approval has been taken. Every woman will be told about the study's purpose and design as well as the significance of evaluating CRP levels in predicting preterm birth after informed, valid and written consent has been obtained. We have applied for funding from the ICMR, synopsis concession, and intramural grant. Each group will be observed for a total of 113 patients who meet the inclusion and exclusion criteria. Serum C-Reactive Protein levels will be assessed between weeks 14 and 20 of pregnancy, followed through birth, and then divided into preterm and non-preterm groups depending on gestational age. Detailed obstetric, menstrual, past, personal, and family history will be taken.

To evaluate the serum C-reactive protein concentrations between 14 and 20 weeks of gestation, venous blood samples from the patient will be taken. To avoid haemolysis, the serum will be removed as quickly as possible and kept frozen until the lab analyses the samples. In a test tube without anticoagulant, samples will be collected and allowed to clot.

A highly sensitive quantitative immunoassay (ELISA) will be used to measure the amounts of C-Reactive protein. A reference level of 1.5 mg/dl is taken. Therefore, pregnancies with high maternal serum CRP levels will be defined as those in which the maternal serum level CRP is above 1.5 mg/dl. Preterm labour is associated with increased maternal serum c-reactive protein. The normal CRP levels during preterm labour and raised CRP levels during preterm labour will be compared.

Discussion

CRP is an acute phase reactant protein that is largely made in liver cells in response to proinflammatory cytokines including IL-6 and alpha TNF. The presence of intrauterine infection is related with C-reactive protein in maternal peripheral circulation. Subclinical amnionitis and preterm birth are associated with its elevated levels in maternal serum. A significant connection was seen between CRP plasma concentrations greater than 1.5 mg/dl.⁵

A study by Shahshahan and Rasouli showed that measuring maternal CRP concentrations can be a useful biomarker for predicting preterm labour. It also showed that, despite the study's patient population's limitations, measuring these women's CRP levels could predict how well these women would respond to tocolytic therapy. However, this finding calls for additional research to evaluate other biologic markers as predictors.⁶

Research by Halder A et al., indicated that a high chance of preterm labour can be predicted by an increased CRP level (>6mg/dl) in early pregnancy in the absence of any obstetric or medical complications. The levels of oligohydramnios, IUGR, and PROM are positively correlated with CRP. The study's weakness is because both pathological and physiological situations cause an increase in CRP. Therefore, further proof is needed to support the widespread use of CRP as a predictor of poor maternal and foetal outcomes.⁷

A study by Grgic G et al., asserts that in pregnant women who do not have any established risk factors for preterm delivery, C-reactive protein (CRP) is a valid marker of idiopathic preterm delivery. The threshold level of CRP that was linked to the emergence of idiopathic preterm birth was 4 mg/L. A link exists between CRP and low birth weight in babies.⁸

Research by Pitiphat W et al., states that in early pregnancy, CRP levels more than 8 mg/liter were linked to preterm birth, regardless of the presence of several other risk factors. The connection was mainly significant for unplanned premature birth. These results back up the theory that persistent low-grade inflammation may increase CRP levels and result in preterm birth.⁹

A study by Hvilsom GB et al., shows that higher CRP levels in the early stages of pregnancy are linked to an increased risk of premature delivery. They have not found a clinical test that can be utilized on all pregnant women in the early stages of pregnancy because the sensitivity and specificity vary depending on the chosen cut-off number. They did note, however, that a small subgroup of women who had CRP levels above 9.9 mg/l but had never given birth prematurely did have a greater chance.¹⁰

Research of Ghezzia et al., (2002) demonstrated that compared to pregnant women who delivered at term, those who had premature deliveries (before 37 weeks gestation) had greater levels of CRP in their amniotic fluid. This research adds to the theory that early-stage intrauterine inflammation or subclinical conditions may play a significant role in the risk of premature birth.¹¹