bbt dip

Louise
Hi ladies looking for some advice on my chart.. I do bbt almost every month apart from the months I take a break from ttc, yesterday 7dpo I got a temp dip of 0.3 and today has took a spike up to 0.33 iv never had this dip at this stage on charting, I was wondering how many women actually get this and not be pregnant? iv read up on some reaserch about it and fertility friend did a survey 11% of women got this dip and wasn't pregnant so it wasn't all that common to see yet 27% got it and all the women were pregnant so it's more common to see in early pregnancy but I'm not wanting to get my hopes up over it