If the leakage is urine, this can be really common due to weakening of the pelvic floor muscles - a result of the weight of the baby in the 3rd tri. I experienced this during the last months of my pregnancy even though I had been doing pelvic floor muscle exercises and pilates weekly! The good news is that I have no lasting pelvic floor issues, no lasting incontinence issues... however it does show the importance of keeping up the exercises.

If the leakage is amniotic fluid, of course it is really important to get it checked out and monitored.

I did read somewhere that there are or can sometimes be, 2 fluid sacs, the main one surrounding the baby and a posterior, smaller one which can break and leak without any danger to the baby. Not sure if this is true or not though and as always, it is always best to get things checked out as has been previously suggested.