Figure 1.

A woman's risk of preterm delivery (PTD), by history of PTD in her own family and in her male partner's family, Denmark, 1978–2004. Female members of the woman's family and her male partner's family who delivered live children before the woman herself in the period 1978–2004 after gestations of known length were included in the analyses. A history of PTD was defined as having 1 or more female family members in the category in question with children born at or before 36 completed weeks’ gestation and before the birth of the woman's child. The risk ratios compare the risk of PTD in women with a history of PTD (≥1 PTD) in the specified female family members with the risk in women with no such family history. The open circles identify risk ratios related to a history of PTD in female relatives on the woman's maternal side. CI, confidence interval.