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

Abstract

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.

Keywords: Cardiovascular mortality; diabetes; offspring birthweight.

Figure 1

Maternal (A) and paternal (B) Hazard Ratio (HR) with 95% Confidence Interval (C. I.) for cardiovascular death (CVD) by offspring birth weight in singleton first births in Norway (1967–2002) with follow-up to 2009. Estimates were adjusted for maternal age and year of birth (711 726 mothers of which 2279 died and 700 212 fathers of which 10 163 died).

Figure 2

Maternal Hazard Ratio (HR) with 95% Confidence Interval (C. I.) for cardiovascular death (CVD) by z-score by birth weight of first born singleton offspring in Norway (1967–2002) with follow-up to 2009. Estimates were adjusted for maternal age and year of birth and z-score was limited to −4 to +4 (711 726 mothers).

Figure 3

Maternal Hazard Ratio (HR) with 95% Confidence Interval (C. I.) for cardiovascular mortality by z-score by birth weight categories (<−1.5, −1.5 to 1.5 and >1.5) for first born singleton offspring born preterm (A) and term (B) in Norway 1967 to 2002, with follow-up to 2009. Estimates were adjusted for maternal age and year of birth and z-score was limited to −4 to +4 (43341 and 668385 mothers, respectively).

Figure 4

Odds ratio (OR) for diabetes in the second pregnancy by z-score by birth weight categories (<−1.5, −1.5 to 1.5 and >1.5) of singleton first offspring born preterm (A) and term (B) in Norway, 1967 to 2002. Estimates were adjusted for year of birth of the second child and maternal age at second birth; z-score was limited to −4 to +4 (35008 and 567116 mothers, respectively).