Cumulative incidence of preterm birth from 24 wk onwards in relation to number of previous abortions for 732,719 nulliparous women, Scotland 1980–2008.

<p>The relative risk of preterm birth for women with zero, one, two, or three or more previous abortions significantly varied across the range 24 to 36 wk gestational age (global test of proportional hazards assumption: <i>p</i> = 0.02). The graph is confined to the risk prior to 34 wk to allow better visualisation of the differences in incidence of extreme preterm births.