Gestational age at 13.8 weeks, fetal heart beat 165& at 18.1 weeks, 155. is my baby gender boy or girl?

No way to know: There is no way to know from your information. The only reliable way is to have an ultrasound or chromosome testing, or wait until he/she is born! the baby's heart beat does not tell you the baby's gender.

Wait 21.9 (+/-2)wks: While there are many wives' tales about predicting baby's gender, all have their flaws. The only way to truly tell is once the little one is born. What a blessed surprise!