Table 2 Key results of the studies.

Study	Endpoints	Results/conclusion
Iheozor-Ejiofor et al., 2017 4	No clear difference in premature births < 37 weeks (RR 0.87, 95% CI 0.70–1.10) between periodontal treatment and no treatment. Low-quality evidence that periodontal treatment may reduce low birth weight < 2500 g (RR 0.67, 95% CI 0.48–0.95). It is uncertain whether periodontal treatment may result in a difference in premature birth < 35 weeks (RR 1.19, 95% CI 0.81–1.76) and < 32 weeks (RR 1.35, 95% CI 0.78–2.32), low birth weight < 1500 g (RR 0.80, 95% CI 0.38–1.70), perinatal mortality (including fetal and neonatal deaths up to the first 28 days after birth) (RR 0.85, 95% CI 0.51–1.43) and preeclampsia (RR 1.10, 95% CI 0.74–1.62).	Total included studies: 15 RCTs Results: When comparing pregnant women with periodontal gum disease who receive treatment to those who do not, there is no clear difference in the number of women receiving periodontal treatment before the 37th week of pregnancy, and fewer babies may be born weighing less than 2500 g (low-quality evidence). Conclusion: There is insufficient evidence to determine which periodontal treatment is better suited to prevent adverse obstetric outcomes.
Manrique-Corredor et al., 2019 16	The meta-analysis gives an OR of 2.01 (95% CI 1.71, 2.36), which represents a significant positive correlation between the explanatory and the result variables.	Total included studies: 20 studies Results: The risk of premature birth is doubled by maternal periodontitis. Conclusion: Health and education centers should prioritize this risk factor and implement preventive measures for all women of childbearing potential in order to reduce the frequency of premature births.
Konopka et al., 2012 15	The overall odds ratio for premature birth with a low-weight infant for mothers with periodontitis is 2.35 (1.88–2.93, p < 0.0001). For low birth weight, the total OR is 1.5 (95% CI: 1.26–1.79, p = 0.001), for premature births −2.73 (95% CI: 2.06–3.6, p < 0.0001).	Total included studies: 15 case-control studies, 1 cross-sectional study and 6 cohorts of studies Results: The hypothesis that periodontitis is an independent risk factor for premature termination of pregnancy and/or low body weight in newborns needs to be further examined. Conclusion: Dental care for pregnant women should be established as an integral part of the prenatal care program.
Da Rosa et al., 2012 14	Treatment of periodontal disease during pregnancy has no significant effect on the overall birth rate of premature birth < 37 weeks (RR = 0.90, 95% CI: 0.68–1.19; p = 0.45; I2: 74%). There is a weak correlation between the treatment of periodontal disease during pregnancy and the reduction of low birth weight < 2500 g, and without a significant effect (RR = 0.92, 95% CI: 0.71–1.20; p = 0.55; I2: 56%).	Total included studies: Outcome premature births: 13 studies included; outcome low birth weight: 9 studies. Results: Treatment of periodontal disease during pregnancy cannot provide general protection against premature birth and low birth weight. Conclusion: Primary periodontal treatment during pregnancy cannot reduce the rate of premature birth or low birth weight.
Boutin et al., 2013 13	A non-significant correlation between periodontal treatment and premature birth (RR: 0.89; 95% CI: 0.73–1.08) can be determined. Daily use of chlorhexidine mouthwashes is associated with a reduction in premature birth rate (RR: 0.69, 95% CI 0.50–0.95).	Total included studies: 12 studies Results: No significant reduction in the risk of premature birth due to periodontal treatment with tartar removal (scaling) and root planing. However, the mean gestational age and mean birth weight in the intervention groups is significantly higher than in the comparison groups. Conclusion: Chlorhexidine mouthwash as a preventive agent should be further examined.
Polyzos et al., 2010 17	In the high-quality studies, the treatment has no significant effect on the overall rate of premature births (OR 1.15, 95% CI 0.95–1.40; p = 0.15). Treatment does not result in a reduction in the rate of low birth weight infants (OR 1.07, 0.85–1.36; p = 0.55), spontaneous abortions/stillbirths (0.79, 0.51–1.22; p = 0.28) or overall adverse pregnancy outcomes (premature births < 37 weeks and spontaneous abortions/stillbirths) (1.09, 0.91–1.30; p = 0.34).	Total included studies: 11 studies Results: Treatment of periodontitis with tartar removal (scaling) and root planing in pregnant women has no significant effect on the incidence of premature births. Low-quality studies indicated a positive effect of the treatment, while high-quality studies clearly show that there is no such effect. Conclusion: Treatment of periodontal disease with tartar removal (scaling) and root planing cannot be considered an effective means of reducing premature birth rates.
Moliner-Sánchez et al., 2020 8	Statistically significant values (RR = 1.67 [1.17–2.38], 95% CI) and low birth weight (RR = 2.53 [1.61–3.98], 95% CI) are determined for the risk of premature birth in pregnant women with periodontitis. A meta-regression, in which these results are related to the income level of the individual countries, gives statistically significant values for premature birth RR = 1.8 (1.43–2.27) 95% CI and for low birth weight RR = 2.9 (1.98–4.26) 95% CI. The risk of premature birth in women with periodontitis is increased by 1.67 times and the risk of a newborn with low birth weight by 1.42 times (evidence level 2a).	Total included studies: 11 studies Results: A statistically significant correlation between periodontitis and the two birth complications studied is found when examining the relationship between these results and the country’s per capita income. Conclusion: These results may not only be due to income, but also due to other factors such as educational attainment, and should therefore be examined in more detail in future studies.