<jats:p><jats:bold>Background:</jats:bold> There is evidence of reduced antioxidant (AO) defense in periodontitis and pregnancy and adverse interactions between periodontitis and pregnancy.</jats:p><jats:p><jats:bold>Methods:</jats:bold> In this study, serum and gingival crevicular fluid (GCF) total AO capacity (TAOC) and superoxide dismutase (SOD) enzyme concentrations in pregnant patients with chronic periodontitis (CP) were compared to those in non‐pregnant patients. Periodontal examinations were performed and GCF/serum samples were obtained from 33 pregnant patients with CP (PCP), 18 pregnant patients with gingivitis (PG), and 21 periodontally healthy pregnant controls (P‐controls), monitored in the first and third trimesters; 27 non‐pregnant women with CP; and 25 non‐pregnant control women. The concentrations of TAOC (automated measurement method) and SOD (spectrophotometric method) were determined.</jats:p><jats:p><jats:bold>Results:</jats:bold> Periodontal parameters were higher in pregnant patients versus non‐pregnant patients and in the CP group compared to controls, whereas TAOC and SOD concentrations were lower (<jats:italic>P</jats:italic> <0.05). All parameters, except plaque index, increased in pregnant subjects in the third trimester compared to the first trimester, whereas TAOC and SOD levels decreased (<jats:italic>P</jats:italic> <0.05). Periodontal parameters were highest and TAOC and SOD levels were lowest in the PCP group in the third trimester (<jats:italic>P</jats:italic> <0.05).</jats:p><jats:p><jats:bold>Conclusions:</jats:bold> Systemic and local GCF AO levels decreased in pregnancy and periodontitis, and AO defense reached the lowest levels in the last phase of pregnancy, whereas periodontal status deteriorated. These results suggest that reduced AO capacity may be associated with adverse periodontitis–pregnancy interactions, and each situation can be a provocative risk factor for the other.</jats:p>