Young men who were born prematurely may have an increased risk for hypertension that is proportionate to the degree of prematurity at birth, according to a Swedish study published in the November 22 issue of Circulation.

“In this study, pre-term birth was identified as a new and very early risk factor for high blood pressure,” said Stefan Johannson, MD, lead author of the study and a neonatologist at the Karolinska University Hospital in Stockholm. “The risk was particularly high among young men who were born at least eight weeks early.

“The association between pre-term birth and high blood pressure is unlikely to be explained by family history or genetic factors. Instead, early environmental challenges faced by the premature baby may affect development permanently, contributing to higher blood pressure in adulthood.”

In Sweden, about 6 percent of pregnancies end prior to term. The corresponding figure in the USA may be as high as 12 percent, according to the authors. Study participants were men born to a predominantly Caucasian population. The authors noted additional research is required to determine whether the results can be generalized to other ethnic and racial groups.

The study involved 329,495 men born between 1973 and 1981 and drafted for military service between 1993 and 2001. Their blood pressure was measured when they were drafted.

Compared with peers who were born at full term (37 to 41 weeks), men who were born extremely pre-term (less than 29 weeks) had almost twice the risk for high systolic blood pressure, very pre-term (29 to 32 weeks) men had a 45-percent increased risk of high systolic blood pressure, and moderately pre-term (33 to 36 weeks) men had a 24-percent higher risk for high systolic blood pressure.
Being born small for gestational age was also associated with a 10-percent increased risk for high systolic blood pressure compared with birth weight appropriate for gestational age.

“In contrast to other studies, we were primarily interested in studying the effects of pre-term birth weight on blood pressure, not low-birth weight,” said Johansson. “Some studies linking low birth weight to cardiovascular disease were based on older people who were born when most very pre-term infants died.”

Although the research does not reveal causes for the association between pre-term birth and hypertension, the authors offered the following suggestions: “[we] believe that very pre-term born children should have their blood pressure checked during their clinical follow-up programs, which matches recent American recommendations. It may also be even more important for people born pre-term to have a healthy lifestyle and to manage known risk factors of cardiovascular disease such as smoking.”