Serum relaxin and beta hCG levels in pregnant women with prior recurrent pregnancy loss and composite adverse pregnancy outcomes

To analyse maternal serum relaxin and β-hCG in pregnant women with a history of recurrent pregnancy loss (RPL) and compare them with a healthy control group without a history RPL. A prospective cohort study was conducted among pregnant women with prior RPL ( n = 47) and healthy controls ( n = 94). Serum relaxin and β-hCG concentrations were measured between 8 and 20 weeks of gestation. Receiver operating characteristic (ROC) curves were generated across the entire study population followed up till birth ( n = 136, combining RPL and control groups) to evaluate the predictive performance of relaxin and beta-hCG for composite adverse pregnancy outcomes. Multivariable binary logistic regression was performed to adjust for potential confounding variables. Mean levels of relaxin and β-hCG were significantly lower in the RPL group (95.28 ± 24.90pg/mL and 425.24 ± 147.57mIU/mL) than in controls (111.61 ± 41.43pg/mL and 542.26 ± 97.97mIU/mL, respectively; p < 0.001). Across all participants, a serum relaxin cutoff < 109.14pg/Ml was a statistically significant predictor of composite adverse pregnancy outcomes (AUC = 0.63; sensitivity = 72.00%; specificity = 55.00%; p = 0.01). Conversely, β-hCG < 540.48mIU/mL was not predictive (AUC = 0.55; sensitivity = 59.00%; specificity = 58.00%; p = 0.30). In multivariable logistic regression, repeat miscarriage (aOR = 31.01, p < 0.01) and caesarean birth (aOR = 3.92, p = 0.01) remained significantly associated with prior RPL after adjusting for maternal age, BMI, gestational age at sampling, and socioeconomic status. Although maternal serum relaxin levels are significantly lower in women with prior RPL, their predictive performance across the general cohort is modest (AUC = 0.63). Relaxin represents a potential candidate biomarker that warrants validation in larger, longitudinal cohorts.