Background and Aims: In periodontal disease, pathogenic inflammatory factors hold a vital part in adverse pregnancy outcomes. In recent years, there has been a large amount of literature concerning the association between periodontal disease and adverse pregnancy outcomes such as preterm birth (PTB) and low-birth-weight baby (LBWB). In the Middle-east region, reports indicate a higher rate of adverse pregnancy outcomes, and periodontitis is believed to be one of several risk factors for adverse pregnancy outcomes. This cross-sectional, epidemiological study aimed to investigate the prevalence of periodontal diseases among pregnant women in the Qassim region and its association as a possible risk factor for adverse pregnancy outcomes. Materials and Methodology: This was a cross-sectional, epidemiological study of 380 pregnant women from the 8th week postconception to parturition who were attending to Maternal and Children's Hospital in Buraidah, Qassim, KSA. The data were collected through questionnaire and oral examination. Plaque scores (Silness and Loe) and gingival disease scores (Ramfjord Periodontal Disease Index [PDI]) were used to assess oral hygiene status. The questionnaire data collected included gestational age, plaque control habits, previous incidences of premature birth, and awareness of expectant mothers about periodontal disease. Results: Data were collected for 380 participants. Our results based on the plaque index and PDI showed that all (100%) of these 380 pregnant women suffered periodontal diseases (gingivitis 78.9% and periodontitis 21.1%). The distribution of gingivitis was the highest among 3rd trimester patients and lowest among 1st trimester patients. Mild-to-moderate types of periodontitis (4 mm–5 mm) were more prevalent among the participants compared with severe (more than 6 mm) forms of periodontitis with a higher prevalence in the 3rd trimester (7–9 months) of gestational age. Conclusions: A very strong significant association of pregnancy and periodontal disease in the Saudi population (Qassim Region) and periodontal disease is risk factor for PTB and LBWB for these patients.