Background: Hypertensive disorders of pregnancy are more frequent in primiparous women, but may be more severe in multiparas. We examined trends in stillbirth and neonatal mortality related to pregnancy-induced hypertension (PIH), and explored whether mortality varied by parity and maternal race.
Methods: We carried out a population-based study of 57 million singleton live births and stillbirths (24–46 weeks' gestation) in the United States between 1990 and 2004. We estimated rates and adjusted odds ratios (ORs) of stillbirth and neonatal death in relation to PIH, comparing births in 1990–1991 with 2003–2004.
Results: PIH increased from 3.0% in 1990–1991 to 3.8% in 2003–2004. In both periods, PIH was associated with a higher risk of stillbirth and neonatal death. We explored this in more detail in 2003–2004, and observed that the increased risk of PIH-related stillbirth was higher in women having their second or higher-order births (OR = 2.2 [95% confidence interval = 2.1–2.4]) compared with women having their first birth (1.5 [1.4–1.6]). Patterns were similar for neonatal death (1.3 [1.2–1.4] in first and 1.6 [1.5–1.8] in second or higher-order births). Among multiparas, the association between PIH and stillbirth was stronger in black women (2.9 [2.7–3.2]) than white women (2.0 [1.8–2.1]).
Conclusions: A substantial burden of stillbirth and neonatal mortality is associated with PIH, especially among multiparous women, which may be due to more severe PIH, or to a higher burden of underlying disease.