Testing before AF

All my cycle calendars say I'm due my period anytime between the 29th of feb & 4th of March but I'm VERY irregular so it usually turns up a week to a week and a half late which would be anytime between the 7th March and the 10th. My fertile window started on the 11th and ended on the 16/17th I'm sure I officially ovulated on the 15th. I go on holiday on the 6th of March and IF I'm pregnant I'd rather know before I go so I can take precaution with food, alcohol etc.. If I was to take a first response or clear blue (ones before your period) what are the chances it would show I was pregnant despite the fact I'm very irregular?