Purpose: The aim of this study was to evaluate the association between periodontitis and preterm birth in a Spanish Caucasian population, based on clinical and biochemical outcomes. Epidemiological studies have suggested that periodontitis is a potential risk factor for preterm birth. However, other studies have shown high heterogeneity in their results. Some factors such as number of evaluations during pregnancy, sample size, study population and maternal age may have an impact on the variability of the result. Methods and Materials: This cohort study enrolled 158 pregnant women, 39 with periodontitis and 119 without periodontitis. All pregnant women were evaluated in the first, second and third trimester. Results: Statistically significant differences were found in periodontal parameters between both groups, but no statistically significant differences were found in biochemical parameters during pregnancy. The duration of pregnancy in healthy patients was 38.78 ± 4.49 weeks, and in patients with periodontitis 37.81 ± 4.89 weeks, with no statistical difference (p > 0.05). This showed that periodontitis was not associated with preterm birth in a Spanish Caucasian cohort. Conclusion: In this study, periodontitis stage II, grade B, was not statistically associated with preterm birth. Pregnancy is a short period of time in order to evaluate long-term oral systemic infections. Adverse pregnancy outcomes are more difficult to occur. Thus, since pregnancy timing average cannot be changed, the stages of periodontal disease (initial, moderate, advanced) could be another factor to study.