brown discharge in 2nd trimester

has anyone experienced brown discharge in their 2nd trimester or later? I'm 18w5d and last night and this morning I noticed brown discharge in my underwear and when I wipe. no cramping, I can still feel some baby flutters, and I can hear baby's heartbeat (I have a doppler). but should I be concerned? I know brown is old blood, but I had 2 previous MCs around 8weeks that started with brown blood and then picked up to red eventually. I just want to know if I can do something to prevent anything at this stage compared to being in the first trimester.