(HealthDay News) – Women with arteriovenous malformations (AVMs) in the brain have a significantly increased risk of rupture and bleeding during pregnancy.

Bradley A. Gross, MD, and Rose Du, MD, PhD, from Harvard Medical School in Boston, reviewed the records of 54 women with an angiographic diagnosis of an AVM. The ratio of the number of bleeds to total number of patient-years of follow-up was used to calculate annual hemorrhage rates.

The researchers found that there were five hemorrhages in four patients over 62 pregnancies, resulting in a hemorrhage rate of 8.1% per pregnancy or 10.8% per year. Twenty-eight hemorrhages occurred over the remaining 2,461.3 patient-years of follow-up, yielding an annual hemorrhage rate of 1.1%. There was a significant risk of hemorrhage during pregnancy (hazard ratio, 7.91), which increased when the analysis was limited to patient follow-up up to age 40 (hazard ratio, 18.12).

“The risk of hemorrhage from AVMs during pregnancy is significantly elevated (hazard ratio, 7.91),” the authors write. “This study evaluated a full cohort of women with AVMs to back-calculate the risk of hemorrhage during pregnancy. Although limited by its retrospective nature and the assumption of AVM presence since birth, we demonstrate an 8.1% AVM rupture rate during pregnancy.”

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