Figure 2.

The association between the known risk factors for preterm birth and the cumulative preterm birth rate. (A) Comparison based on presence or absence of bacterial vaginosis (BV) in the first trimester. (B) Comparison based on presence or absence of BV in the second trimester. (C) Comparison based on presence or absence of a past history of preterm birth. (D) Comparison between smokers and non-smokers during pregnancy. (E) Comparison of four groups divided by maternal age. (F) Comparison between multipara and primipara.