Ms Shelly,
I am the product of exactly what you are considering.
The most awesome thing about it is my feelings towards my dad for his love for my mom. He loved her so much that he let her have a child that wasn't his. I never knew until I was 17 or so. My mom brought it up because he and I weren't getting along. She thought that might have been the reason. Looking back the real reason was the lack of God in my parents' life. She's went through the same guilt trips that many mothers go through when a child begins to grow up and get into some stuff they shouldn't (blaming herself and so on). Unfortunately, she has in addition to what some other mothers go through, attempts by a spirit in her life that makes her feel guilty about ever having me. I'm grateful she did. I'm grateful my dad played his role in it. But at the same time, it's not the mother and father that place the soul in the child, it's God.
The best thing is just to be right with God before taking any other steps. Don't leave an open door to an spirits of condemnation. If either you or your husband is holding onto any sin then that's exactly what you're doing. I don't you so I'm not saying either or you are doing so. And by holding onto sin, I'm not saying messing up and getting back up. I'm just saying this so that you do not fall into some of the problems my mom has had.
My parents never told anyone in the family. My mom has told some of her sisters after my dad died, but the thing is it's none of their business unless you want it to be. If you do tell them, their reception of it should be an indication of where they are in Christ. At the same time, even if they are opposed and make it known, it's still your place to love them. That's a tough spot that could only be won over by Christ in you, loving someone who feels negatively (to put it lightly, may be worse) about your child. Not to say they'll be negative, they may very well accept it. Point is this is another place you want yourself and your husband right with God.
Lastly, when it comes time to tell the child. Don't do it anger or alone. You both need to be there. My dad was hurt by that. Oh, and in the end after I knew he wasn't my biological father and yet he still worked sometimes 100 hours a week so I could have more than he had when he was young, that made me respect him and love him all the more. My parents finally got close to God before my dad died. He and I got close the last three months he was still on this earth, it was a wonderful time.
Be encouraged. Yes, pray about it. Everyone believes God COULD but few believe God WILL. When you start believing He will, you start expecting it. If you were to expect God to give you a new car and your garage was a mess, what would you do? You would clean it out. Expectation comes with action. There's nothing wrong with you going through scientifical means to bring a child into the world, all good things are given of God. Likewise, things God gives for good, satan attempts to corrupt and use it for sin. If your child is sick, yes, take them to the doctor. On the way, pray and expect the doctor to say the child is ok. But sometimes it's through suffering that we recieve blessings. Suffering many times produces growth in a man. In John 15, Jesus tells of God as the pruner. Tell me, what bush if it had a nervous system wouldn't hurt during pruning. But out of suffering comes perseverance, and to that character, and to that hope, and hope never fails. Perhaps you and your husband should ask God once again for a child. Thank Him for the child and then go and get ready for the child. Get the room ready, get some clothes and so on. You may have to wait, and it may come down to science, but keep trying during all of that time out of a trust in what God is going to do. At the very worst, you'll have nice stuff to donate to someone who can't afford it. There's even a blessing in that. So you can't lose! Be encouraged.
Do what you want and if you talk to God about it and don't feel convicted go for it