I remember hearing so many old wives' tales about this! In my first pregnancy the heart rate was always around 160 and I had an anterior placenta – some people swore that meant a girl, but I ended up having a boy. With my second the heartbeat was slower and I still had a girl. The only reliable way to know is through ultrasound or blood tests like the NIPT after 12 weeks. Placenta position and heart rate vary from baby to baby, and both boys and girls can have heart rates in the 120‑180 range depending on activity. It's fun to guess, but try not to read too much into it.