I had little brown discharge at 17 weeks. Doctor advised me for cervical scan.?

The cervix is 3.8cm with no funneling which i hope is gud. What's the normal length of cervix? But i am still confused what can be the reason of the dicharge? What was your baby's heartbeat at 17 weeks, is 142 bpm good?Everything else is perfect for my pregnancy. Do i need to worry? Girls,pls help.