what is the minimum value of specific gravity in patient 16572's body until 66 months ago?
select min(labevents.valuenum) from labevents where labevents.hadm_id in ( select admissions.hadm_id from admissions where admissions.subject_id = 16572 ) and labevents.itemid in ( select d_labitems.itemid from d_labitems where d_labitems.label = 'specific gravity' ) and datetime(labevents.charttime) <= datetime(current_time,'-66 month')