Objective: Preterm delivery may predict an increased risk of cardiovascular disease in mothers, providing opportunities for prevention. No study had examined whether gestation length within the term period predicts future CVD, and there are few data segregating spontaneous from medically indicated deliveries.
Study design: We used proportional hazards models to predict CVD death by gestation length, adjusted for age, education, and delivery year among 688,662 women with births from 1967 through 1998 in the Medical Birth Registry of Norway. Mothers were traced in the National Cause of Death Registry through 2009; there were 2324 CVD deaths.
Results: Compared with women who delivered spontaneously at 39-41 weeks' gestation, women who spontaneously delivered earlier had higher risks of CVD death. Hazard ratios were 1.9 at 22-31 weeks, 2.2 at 32-34 weeks, 1.6 at 35-36 weeks, and 1.4 at 37-38 weeks. Risks were higher among women with medically indicated deliveries (hazard ratio, 4.8 at 22-31 weeks, 2.7 at 32-34 weeks, 4.3 at 35-36 weeks, and 1.6 at 37-38 weeks compared with spontaneous deliveries at 39-41 weeks). Neither spontaneous nor indicated delivery after 41 weeks was associated with CVD mortality. Risks were highest with recurrent preterm pregnancies, and for women who delivered only one child, especially if that delivery was preterm.
Conclusion: Women who deliver spontaneously before 37 weeks had a 2-fold increased risk of CVD mortality compared with women who had delivered after 38 weeks. Even women with spontaneous deliveries at early term (37-38 weeks) had a 41% elevated risk of CVD death compared with women delivering at 39-41 weeks.
Keywords: cardiovascular diseases; epidemiology; pregnancy; prevention; risk factors.
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