I'm not ttc but I use bbt as part of my contraception (very effectively by the way!).
But this heatwave I'm sure is throwing my bbt out of whack. Today for example my measurement was 36.54 but I got my period (as expected, I'm usually 24-27days). Usually I'll see a much lower drop down to around 36.40 or lower to warn me of my period starting. Likewise my ovulation wasn't so marked because my temps are high anyway.
Anyone else noticed this?