Just came from my appointment and the OB said on my next appointment they’ll do a swab? Then I’ll be…

Just came from my appointment and the OB said on my next appointment they’ll do a swab? Then I’ll be going every week from there, I don’t remember getting a swab with my previous pregnancy and I was too excited to ask lol any mommas know any information on this? I’ll be 36 weeks my next appointment.