Being born too small, too early, or both: Does it matter for risk of hypertension in the elderly?

BACKGROUND Low birth weight is an often-reported risk factor for high blood pressure later in life. This study investigates the selective contributions of preterm birth and poor fetal growth to later risk of hypertension. METHODS A total of 250,000 Swedish birth records from 1925 through 1949 were examined. All subjects born with a gestational duration below 35 weeks and/or a birth weight <= 2,000 g (girls) or <= 2,100 g (boys) were included, as well as an equal number of controls. This yielded a cohort of 6,269 subjects, of which 2,502 were born at <35 weeks of gestation, and 1,226 subjects had a birth weight <= 2,000 g (girls) or! 2,1 00 g (boys). The main outcome measure was diagnosis of hypertension in the Swedish Hospital Discharge Register from 1987 through 2006. RESULTS There were 838 cases of hypertension in the cohort. Birth weight was negatively associated with hypertension (P for trend = 0.0005). This effect was explained by poor fetal growth: when compared with subjects with a normal fetal growth, those born small for gestational age had a 54% increase in risk of hypertension. In contrast, there was no association between gestational duration and hypertension. CONCLUSION For those born in the first half of the twentieth century, the association between low birth weight and adult hypertension is due to poor fetal growth and not due to preterm birth.