Abstract Introduction Periodontal diseases (gingivitis and periodontitis) are chronic non‐communicable inflammatory diseases. The risk of developing gingivitis and periodontitis increases during pregnancy. Also, periodontitis increases the risk of developing adverse pregnancy outcomes such as preterm birth and preeclampsia. Early diagnosis of adverse pregnancy outcomes is essential and periodontitis could be an early sign to take into consideration. Material and methods We conducted a longitudinal observational study (PERISCOPE study: CNIL, no. 1 967 084 v 0; CER, no. 01–0416) on 121 pregnant women in the first trimester to determine their oral and periodontal health status. We explored the relations between oral and periodontal health status and sociodemographic and behavior characteristics, as well as their course and outcome of pregnancy. Results A total of 47.1% of the women had periodontitis, of which only 66.7% presented clinical manifestations associated with the disease such as gingival bleeding. These women had a poorer oral and periodontal health, and a higher body mass index, and more of them developed gestational diabetes during the course of pregnancy. The remaining 33.3% showed only discreet and isolated inflammatory signs and, unless thoroughly examined, would have gone undiagnosed for periodontitis. Interestingly these women were more often primiparous, still active professionally and had had a recent oral examination. Conclusions The PERISCOPE study is one of the few studies that reports the oral and periodontal health status of pregnant women in the first trimester. Furthermore, the results highlight the need for early oral and periodontal assessment and treatment, even in the absence of exterior clinical signs, in order to prevent periodontal disease aggravation and also, by reducing low grade systemic inflammation, possibly adverse pregnancy outcomes.