I'm 37 weeks and 3 cm dilated and i lost my mucus plug today how much longer tell labor starts?

Very variable: Some patients will go into labor in a few hours, others may not start labor more than a few days. If your contractions start getting closer (every 4-5 minutes), or you start leaking fluid call your doctor. You may spot , but heavier bleeding should also prompt a call.

No one knows: The loss of the mucous plug means that your body is getting ready for labor, but sadly does not predict exactly when it will start. It could be tomorrow or 3 more weeks.