I think it is to the point of an addiction or a strange obsession. They have always said they would take whatever children God gave them, but to "try" for #20 is different. They shouldn't have to "try." If God is going to give them another child, it will happen. Their friends the Bates were also actively "trying" for #19 or so a while back too. They were actually intervening to try to get pregnant again even though they didn't have health insurance!
To me that voids the whole notion that they take what God gives. If he's done giving, he's done giving. Enough already!