I think boy and think they have known for a while. It makes no sense that they paid to get the screening blood test with the last 2 that also tells you gender at about 10 weeks, but wouldn't pay for it this time when she's even higher risk due to being older.
I know people think they would love it if they found out their child had something that would require more medical care because of the click bait but they really wouldn't. As shown with Mila and Jace, they want to use hospital visits for vlogs only when it suits them. They want to put themselves and holidays first. Any child needing more appointments either after they are born or during pregnancy wouldn't stand a chance and they know would only lead to more professionals being involved in their life, possibly for ever.