Eh, 12-13 hours is quite long lah at 18 weeks, definitely boleh, but make sure you stop every 2-3 hours to stretch your legs and walk around a bit, okay, because sitting too long during pregnancy can cause blood clots. A few of us did long drives during second trimester and honestly the discomfort was more the problem than anything else, cushion under your back helps a lot! But since you're carrying, best to check with your gynae first to make sure everything is progressing well and ask them if there's anything special you should do for a drive that long. Minum plenty of water and jangan skip meals, and of course have your husband drive so you can rest.