From the article:
Oestrogen helps maintain the structure of blood vessel walls by promoting the division of endothelial cells within the vessel walls, which is important for repair if the vessels become damaged. However, oestrogen levels drop significantly at the menopause.
Women have been shown to be more likely to develop a cerebral aneurysms after the age of 40 years, and aneurysms are most likely to rupture between the ages of 50 and 59 years.
The authors asked 60 women with cerebral aneurysms about their use of the oral contraceptive pill and hormone replacement therapy, and this was compared with usage in 4,682 other women drawn from the general public.
Women with cerebral aneurysms were found to have been significantly less likely to have taken oral contraceptives or hormone replacement therapy. Women with cerebral aneurysms also had an earlier average age of menopause.
Previous studies have shown that use of the oral contraceptive pill protects against haemorrhagic stroke in later life, while women who start their periods early and/or do not have children are at greater risk.