Hehe, congrats on your pregnancy! Honestly, heart rate alone isn't reliable, a few of us tried guessing based on bpm and lahat ng guesses namin ay mali haha, so I wouldn't bet on it. The nub theory (looking at the angle of the genital tubercle) is more fun to try if you want to guess, but really the safest bet is waiting for the anatomy scan or asking your OB kung makikita na niya clearly, kasi sa 18 weeks still kinda early for some babies to cooperate! As for the nose, that part is tricky to point out sa ultrasound kasi ang baby's face is usually at an angle na mahirap makita clearly, your sonographer would be the best person to help you identify features. Good luck, mama!