North American Menopause Society
( thought I'd have a look at what the experts say and this phrase caught my eye. UK's official menopause orgs presumably operate on basis of the same medical research)
“window of vulnerability”
'Theories exist as to why women have double the rates of depression during this period. One theory is that there is a “window of vulnerability” such that some women are more sensitive to the hormone shifts that occur during perimenopause and puts them at greater risk for depression. In addition, women at greatest risk are those with a history of depressed mood earlier in life.'
www.menopause.org