Background and aims Pregnancy represents a complex state in which the mother and the fetus both contribute to the oxidative stress and production of reactive oxygen species. The ability to buffer these is called total antioxidant capacity (TAC). We aimed to evaluate whether amniotic total oxidant status (TOS) and TAC can have a role in late preterm births after premature rupture of membranes (ROM).

Methods The study was a prospective observational trial. Group 1 (n = 30): late preterms with premature ROM, Group 2 (n = 30): term infants with prolonged ROM, Group 3 (n = 30): term infants born without prolonged ROM. Amniotic fluid and cord blood samples were collected during delivery and TOS(µmolH₂O₂ Eq/L) and TAC(mmol Trolox Eq/L) levels were measured.

Results Mean gestational ages were 35,3 ± 1,1; 39,29 ± 1,25; 38,7 ± 0,63 weeks respectively. Cord blood samples of the groups revealed no difference between any of the parameters checked (pH, pCO₂, HCO₃, lactate, Methb, TAC and TOS) (p > 0.05, for each). TAC levels of amniotic fluids (2,05 ± 0,60; 2,04 ± 0,5 and 21,89 ± 0,36) were also similar between groups (p > 0.05). But TOS levels of Group1 was significantly higher than Group2 (p < 0.05) and Group3 (p < 0.01). No significant difference was detected between Group 2 and 3.

Conclusion Similar cord blood levels of all parameters reflect the similar perinatal conditions of infants at birth. Similar TOS levels of term groups show that there is no close relation between TOS and infectious status. But on the other hand; significantly higher TOS levels of Group1 can be related with premature birth; which can lead us to antioxidant therapies to avoid premature birth.