Heartbeat dropped to 115??!

Hi ladies! Im 31+4 Weeks with baby boy and his HR was always ranging between 125-130. Im not high risk so I will not have any third semestre scan. At my appointment today HR was 115... I know its still over the 110 minimum but I wonder why the sudden drop. It makes me anxious to err on the lower limit side... Doc did not look concerned so I dont want to obsess about it but have this happened to anyone? I would understand if I was really closer to delivery but I still have 8 weeks to go and baby's HR can't really drop anymore...