3rd Trimester Spotting?

Has anyone had 3rd trimester spotting? What was your outcome/diagnosis? I'm 32 weeks now and had bright red spotting at 31 weeks. I saw my doctor a couple days after that and he did a ultrasound on my placenta. There were no tears or any sign of bleeding. After that he sent me down to the labs for blood work since my daughter is measuring 3 weeks behind. This is my 3rd pregnancy and first pregnancy where I've experienced any type of bleeding during so I was a bit alarmed and still curious of why I had the bleeding in the first place. May also add sexual intercourse was of no cause and the blood did indeed come from my vagina.