nub theory?

Vickie
Hi, so this is my fourth pregnancy (first three being miscarriages) and I've just hit such a massive milestone of going past my 12 weeks and having my 12 weeks scan!❤️❤️ absolutely over the moon but I was wondering if anyone could guess boy or girl with the nub theory? I'm struggling to find it ha! 
Thanks!!
P.s, these are all my baby, just at different weeks up to the 12 weeks!❤️