Going through childbirth more than once appears to raise a woman’s risk of having a stroke due to bleeding in the brain, Korean researchers report.

In a direct comparison of women who did and did not have a stroke, the risk of bleeding, or “hemorrhagic,” stroke rose 27 percent with each additional birth over none or one, Dr. Byung-Woo Yoon, at Seoul National University Hospital in the Republic of Korea, and colleagues found.

Pregnancy and delivery are known to raise stroke risk, the researchers note in the journal Neurology. Multiple births further strain and stress blood vessels and other body systems, and the stress of raising kids may also raise stroke risk.

But additional investigations are necessary to fully understand the actual underlying reasons why childbirth is tied to increased stroke risk over a woman’s lifetime, Yoon and colleagues note.

They looked at ties between childbirth and stroke in a study involving 459 women who had a stroke and 918 who did not. The women were about 56 years old on average at the time of the study.

Among women who had a stroke, 38 had zero or one childbirth, 143 had given birth twice, 107 had given birth three times, and 171 had four or more deliveries.

After allowing for many other factors associated with stroke risk such as age, family history of stroke, high blood pressure, diabetes, cigarette and alcohol use, as well as oral contraceptive and hormone replacement use, each additional birth was associated with 27 percent greater risk for stroke.

Women reporting four or more childbirths had nearly a threefold higher risk of stroke as women with no childbirths or one childbirth.

“Further research concerning the biologic, environmental, and psychosocial basis for this association would be meaningful in order to develop appropriate prevention strategies,” Yoon and colleagues conclude.

In a commentary published with the study, Dr. Michael R. Skilton, at the Heart and Diabetes Institute in Melbourne Vic, Australia, said this study provides strong evidence that childbirth may somehow influence hardening or weakening of blood vessels and he encourages further study of the issue.

SOURCE: Neurology, published online March 24, 2010