Prenatal growth and risk of occlusive and haemorrhagic stroke in Swedish men and women born 1915-29: historical cohort study.

The cohort comprises all 14 611 births in the Uppsala Academic Hospital between 1915 and 1929. Socioeconomic circumstances and neonatal characteristics, including gestational age (number of completed weeks since last menstrual period), were available for 96% of the subjects from hospital records and follow up is 98% complete. Analyses were restricted to singletons born at 30-45 weeks’ gestation for whom information was available in the 1960 and 1970 censuses. Data on occurrence of first stroke were obtained from the Swedish national hospital discharge register and from the national cause of death register. Two subtypes of stroke were defined—haemorrhagic (ICD-8 (international classification of diseases, 8th revision) 430-431; ICD-9 430-432) and occlusive (ICD-8 432-436; ICD-9 433-436). Each participant was considered at risk from the time of the 1970 census to date of first stroke, emigration, death, or end of follow up (31 December 1996). The 10 853 men and women had 991 first strokes—156 haemorrhagic, 775 occlusive, and 60 ill defined. Death certificates identified 41 (26%) first haemorrhagic strokes and 17 (2%) occlusive strokes. Of haemorrhagic strokes, 21 (13%) were subarachnoid and 135 (87%) intracerebral or unspecified intracranial haemorrhages. Cox proportional hazards model showed birth weight inversely associated with risk of haemorrhagic stroke and little evidence of association with occlusive stroke. Hazard ratio per 1 kg increase in birth weight (adjusted for sex and period of birth) was 0.61 (95% confidence interval 0.45 to 0.83) for haemorrhagic stroke and 0.89 (0.77 to 1.03) for occlusive stroke. Adjustment for socioeconomic factors at birth and at the time of the 1960 and 1970 censuses had little effect on estimates (table). When head circumference and birth length were adjusted for separately and in combination, the inverse association between birth weight and haemorrhagic stroke strengthened but there was little effect on the association of birth weight with occlusive stroke. Adjustment for gestational age had no substantive effect on the estimates.