Offspring birthweight by gestational age and parental cardiovascular mortality: a population-based cohort study.

Objective: To estimate risk of parental cardiovascular disease mortality by offspring birthweight.

Design: Population-based cohort study. Setting and population: Norwegian mothers and fathers with singleton births during 1967-2002 were followed until 2009 by linkage to the Norwegian cause of death registry.

Methods: Hazard ratios by offspring absolute birthweight in grams and birthweight adjusted for gestational age (z-score) were calculated using Cox regression and adjusted for parental age at delivery and year of first birth. Stratified analyses on preterm and term births were performed. Main outcome measures: Maternal and paternal cardiovascular mortality.

Results: We followed 711 726 mothers and 700 212 fathers and found a strong link between maternal cardiovascular mortality and offspring birthweight but only slight evidence of associations in fathers. Adjusting birthweight for gestational age (by z-score) uncovered an unexpected strong association of large birthweight (z-score > 2.5) with mothers' cardiovascular mortality (hazard ratio 3.0, 95% CI 2.0-4.6). This risk was apparently restricted to preterm births. In stratified analyses (preterm and term births) hazard ratios for maternal cardiovascular mortality were 1.5 (1.03-2.2) for large preterm babies and 0.9 (0.7-1.2) for large term babies (P-value for interaction = 0.02), using normal weight preterm and term, respectively, as references.

Conclusion: Women having large preterm babies are at increased risk of both diabetes and cardiovascular mortality. The birth of a large preterm baby should increase clinical vigilance for onset of diabetes and other cardiovascular disease risk factors. Tweetable abstract: Birth of a large preterm baby should increase vigilance for cardiovascular-disease risk factors.