Oral Diseases (2012) 18, 648–654 Aim:  Infective agents may affect pregnancy outcomes by deregulating homeostasis. Objectives:  The effects of Porphyromonas gingivalis infection before and at different gestation periods were evaluated. Materials and Methods:  Wistar rats infected via subcutaneous with P. gingivalis W83, one week before mating (BM), days 1 (PR1) and 11 of gestation (PR11), and controls were evaluated, and samples were obtained at the end of gestation. P. gingivalis was detected by PCR. Cytokine was determined by ELISA. Results:  Infected rats had lower maternal gain of weight. Implantation was not observed in 2/12 BM rats. PR11 presented more fetal‐placental resorptions and lower placenta/fetus weight than controls. P. gingivalis was detected in placenta and fetus. IL‐6 and TNF‐α levels were higher in placenta and serum of infected groups, except for TNF‐α in placenta of PR1. IL‐1β levels were higher in placenta of PR11, but lower in serum and placenta of PR1. There were no differences in IL‐10 and PGE2 concentrations among the groups (P < 0.05). Conclusions:  The experimental infection by P. gingivalis resulted in alterations in the gestational pattern and in fetal development. The consequences of infection at mid‐gestation were more severe than at the beginning, possibly due to the induction of pro‐inflammatory cytokines in the fetal compartment.