24 weeks...should i worry?

At this point should i worry about these two deciding its time to come out at 24 weeks. My first was considered late but i think they had the days wrong, i miscarried my second at 16 weeks. I'm just concerned that with my growing twins that they well go "OK its time to come out" I'm a pretty small framed girl so the thought is in my mind a little more each day. Im normally 32 inches at the waist i am now 41inches. I sport a pretty large bust line though. Picture is just for visual guide really. But do i really need to worry?