At my 20 week ultrasound the dr told me that i have a window in my uterus, and should deliver early what does that mean? this will be my 5th csection

Scar tissue: It likely means that you have a section of your uterus that is relatively thin from the scarring from your previous c-sections. That thin section is not as strong as the rest of the uterus, and may be a source of uterine rupture if allowed to stretch too much. Now that your OB knows about it he will be following it carefully.

Ultrasound: Your doctor is referring to a weakness that occurs in the lower uterine segment that can cause thinning of the muscle, such that it appears as a "window". This is caused by multiple c/sections, and inherent weakness of the scar area. The concern with this, is the possibility of a uterine rupture, which is very serious. Thus the talk of early delivery. Hope this helps.