Heartbeat gender prediction

I know this is silly and I know this CANNOT tell me the gender but I have a question about the heartbeat gender prediction. So I’ve heard that the wives tale is that a heartbeat over 140 means girl, but like at how many weeks? Because I’ve gone for 2 ultrasounds already (6 & 7 weeks) and heartbeat is increasing but like initially it was below 140. Does this post even make sense? I’m so confused by this. When they say heartbeat over 140, how many weeks are they talking about?