Background:  Porphyromonas gingivalis (Pg) is one of the most harmful periodontal pathogens and it has been reported that Pg is associated with preterm birth (PTB), intrauterine growth retardation (IUGR) and pregnancy‐induced hypertension (PIH), discovered by animal experiments and clinical research. The relationship between adverse pregnancy outcomes and maternal antibody response to Pg is controversial. On the other hand, the serum C‐reactive protein (CRP) has been recognised as a reliable serum marker of periodontal disease.
Aims:  To determine the significance of antibody responses to Pg affecting pregnancy outcomes in the first trimester.
Methods:  A case–control study was carried out on women with PTB (n = 58), IUGR (n = 91), PIH (n = 32) and without any complications (control, n = 98). The serum level of the CRP and IgG1 against 40‐kDa outer membrane protein of Pg (anti‐40‐kDa OMP Pg‐IgG1) in the first trimester was measured.
Results:  The IUGR group, and PTB patients whose placentas were diagnosed as chorioamnionitis or whose vaginal flora included Lactobacilli, showed a lower level of anti‐40‐kDa OMP Pg‐IgG1 than the control group. There was no difference in the serum CRP level between each case group and control group.
Conclusions:  These results suggest that a lack of humoral immunity against Pg in early pregnancy is associated with IUGR and some PTB.