The smartest ob/gyn (and one time hippy!) I ever met said to call a woman perimenopausal was to say a 2 year old is pre-menarchal...its not a clinically definable,measurable change ....BUT, as a rule, in GENERAL (meaning lots fall out of the spectrum) - "things change," after 35...and its that abrupt...in GENERAL for most women.....can be like me, from 4 periods a year to every month, mood/anxiety changes, ....also by the late 30's/early 40's, comes full development of the frontal lobe which means a heightened sense of perspective (maybe to balance on coming hormonal storm?),sanity, and insight, generativity,etc... I had little blimps of changes in my 30's....at 40, my figure got curvier, but weight didn't change...at 45, blatent thinning of the skin around the eyes, a few gray hairs...47 - woomp - noticable hearing loss, vision loss, and wonky shoulders - menopause induced gimpiness I'm convinced....and STILL a regular period!!!! Oh, an 10 extra pounds....5'5 was 127-132 for YEARS ....now fight to stay 135-142......