Ive been riding the MRT everyday for the first five months of my pregancy. I think it was only during my fifth month that i used the priority lane. I was showing but not as big and my bump can still be hidden on certain styles pf clothes so there were instances when the guards and other passengers were accusing me. I had to be tougher in telling them my situation. Or, if possible, you can get a pregnancy certificate from your doctor as proof.