It's not *entirely* an OWT, but it's certainly not reliable, and I wouldn't assume the u/s was wrong based on it (although if I recall correctly, there was some uncertainty around the gender based on your u/s - unless you had a second one?) From what I've heard and read, later on in pregnancy, boys' heart rates tend to be a little lower than girls' - meaning, around 3rd trimester. It's not something you can go by in 1st or 2nd trimester, though, and I wouldn't "go by" it even in third.
It's likely that it has more to do with your baby's activity level than his or her gender. And, as they get bigger, they have less room to move around, so they are likely to be a little less active, right? So it would make sense that the HR would be lower.
Honestly, I have no clue what mine have been other than the first couple of ultrasounds, where they measure it and tell you. I don't think mine have been consistent with the OWTs, though.
At the same time, it sounds like maybe you didn't get a good, certain confirmation that your baby is a girl, via ultrasound. I think I'd hold off on buying a whole bunch of pink stuff - I'd go with neutral on the things that you HAVE to buy ahead of time, and wait until you know for sure for the things you don't have to get beforehand.
Good luck!
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