I have been taking 50mg of B6 a day since ttc and since BFP, because I heard you weren't supposed to quit taking it after BFP. 

Is there a danger of miscarriage if you take it during 1st trimester?  Do I need to stop taking it?  Or is it okay to continue the 50mg a day?

 Do NOT stop taking it or it could cause a miscarriage.  B6 increases your progesterone and if you suddenly drop your progesterone levels you could miscarry.  Keep taking the 50mg until around 12 weeks and then taper off slowly.  So take 25mg for awhile and then 12mg and then be done with it.

b6 is 100% safe to take during pregnancy and can prevent morning sickness.  If you want to stop taking it then take 50mg for a week, then the next week take 30 mg, then 15 mg then 10 mg then stop.  So this will take 4-5 weeks