This study confirms the association between maternal serum concentration of OCPs and preterm labour, and also reports an increased mRNA expression of inflammatory pathway genes such as TNF-α and COX-2, which have not been correlated with OCPs levels in previous studies concerning preterm birth aetiology. Even if COX-2 and TNF-α cannot be considered as direct biomarkers for pesticide exposure, since these are involved in all inflammatory processes that contribute to the onset of PTB, a possible gene-environment interaction may occur. The association between OCPs with mRNA expression of TNF-α gene should be further investigated.