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. ConclusionWomen 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.Keywords Cardiovascular mortality, diabetes, offspring birthweight.Tweetable abstract Birth of a large preterm baby should increase vigilance for cardiovascular-disease risk factors.

Objective To assess the effects of socioeconomic factors on the association between parity and long-term maternal mortality. Methods This was a population-based cohort study of mothers with births registered in the Medical Birth Registry of Norway (MBRN) during the period 1967 to 2009. We estimated age-specific (40 to 69 years) cardiovascular and non-cardiovascular mortality ratios by number of births using Cox proportional-hazard models. To assess effect modification by mothers’ attained education we stratified on low (<11 years) and high (≥11 years) educational level. We further evaluated fathers’ mortality by number of births using the same analytical approach. Results Mothers with low education had higher mortality (cardiovascular: hazard ratio (HR) 2.62, 95% confidence interval (CI) 2.34–2.93, non-cardiovascular: HR 1.67, 95% CI 1.62–1.73). Among mothers with low education, cardiovascular mortality increased linearly with each additional birth above one, (p-trend=0.02). In contrast, among mothers with high education, cardiovascular mortality declined with added births, (p-trend=0.045). For non-cardiovascular mortality there was no association among mothers with low education, while mortality declined with increasing number of births among mothers with high education, (p-trend<0.01). Father’s mortality showed similar associations with number of births when stratified on maternal education. Conclusions Women’s long-term mortality rose with number of births only for cardiovascular causes of death, and only among mothers with low education. Partners of women with low education had similar increasing risk with increasing number of births. Maternal educational level is a strong modifier of the association between parity and long-term mortality.