BBT and pregnancy

G'day all

My wife has been measuring her bbt as we are TTC, and it started at 37 degrees (98.6F) then 37.3 (99.14F) and then 37.4 (99.32F)

My question is - I read that if your bbt is above 37C (98.6F) for more than 4 days that it is a good sign of early pregnancy/ conception

I am not sure if this is accurate in real life scenarios, so I wanted to know what your experience with bbt charting in relation to pregnancy is - did you get a bbt spike around the time you later found out was the time of conception?

Thanks in advance!!!