I lost my mucus plug at 37 weeks, I was 3cm dilated and 75% effaced. It grew back, and I lost it again at 40 1/2 weeks. And with no sign of baby I was due to be induced at 40 weeks 6 days, but she came a day before at 40 weeks 5 days. Though I've heard of some people losing their plug RIGHT before labor, I unfortunately got my hopes up and had to wait weeks lol ): so be prepared for that