To determine the level of periodontal disease that was
associated with preterm birth, 75 subjects drawn from the
population received periodontal examinations, and attachment
loss was measured. Attachment loss (AL) is a reliable
quantitative measure directly associated with the anatomical
definitions of periodontal disease (Figure 2). Specifi-
cally, for a range of attachment loss thresholds (measured
in millimetres), the number of sites at which AL exceeded
the threshold was counted for each patient at baseline.