Fig 1. Periodontal treatment and preterm birth (PTB).

(A) Conventional meta-analyses were performed to analyze the effect of periodontal treatment in control populations with moderate (<20%) and high occurrence (≥20%) of PTB as well as in the total population. Heterogeneity was assessed using χ²-test and I²-statistics. (B) Trial sequential analysis of trials in population with moderate occurrence of PTB. The cumulative Z-score (black), i.e., the accumulated level of significance, was plotted against the number of participants accrued so far, which was compared with the heterogeneity-adjusted required information size (HRIS). Based on HRIS, the trial sequential monitoring boundary (TSMB) for benefit was plotted (grey oblique). The Z-curve nearly crosses the futility boundary, and HRIS is not reached. (C) Trial sequential analysis of trials in population with high occurrence of PTB. The Z-curve does not reach the HRIS, and does not cross the TSMB.