Welcome to the forum, congratulations!
I haven't been on Humira, but I've had two pregnancies with Remicade, which is a very similar drug. With both pregnancies (done across three different states with three different sets of OBs and high-risk OBs) the consensus is that it's best to stay on the medication the entire pregnancy. It does get into the baby a bit, but it doesn't cause any harm. The baby will be born with a small amount of the medication in their system, but as long as you keep the baby away from the public for a couple of months (which you should kind of do anyway), and don't do any live vaccines for the first year (which in the US is only the rota-virus), then you should be just fine. And since Humira doesn't stay in the system as long as Remicade, I imagine that it's even safer. The study he referred to for all of this is the PIANO study, I believe is what it's called.
My GI mentioned to me that Entyvio (I *think* that's the medication he said) doesn't cross the placental barrier at all, so it should be even better if you want to switch to it. I was already about 5 months along with my second, so I didn't feel comfortable switching in case it didn't work or I flared or something while pregnant.
Also, with regards to breastmilk, the proteins for Remicade (and I am assuming Humira) are too large to get into breastmilk, so it's completely safe to nurse/pump after childbirth.
"For this thing I besought the Lord thrice that it depart from me. He said, My grace is sufficient for thee: for my strength is made perfect in weakness. Most gladly therefore will I rather glory in my infirmities; I take pleasure in infirmities, reproaches, necessities, persecutions, distresses, for when I am weak, then am I strong" 2 Cor