Hiya! I'm so happy you've come here. As I have not posted a lot besides my own question's I've been reading non stop for the last couple of years. I do have some advice (others, let me know if you agree or disagree- I might learn some more.)
I would honestly wait to file until after you deliver. I know medical costs are skyhigh and if you happen to have an astronomical doctor or hospital bill you would include that in your filing. I only say this because during rebuild you dont need a collection's account to open up because this is pretty damaging. I would keep a hold of that $4000 to cover medical cost during/after delivery.
Your husband can feel free to add you as an authorized user now on his cards as your filing will not affect them. They may help "cushion" your score when you do file however, if it is "joint" credit as you agreed to be responsible for the accounts this will be a different story...
As many of us will agree to disagree on the secured card route please read the 700 in 24 months as it is pinned on the bankrupcy thread's as this is what I'm following when I'm discharged in 30 days 
Some more questions though... the $4000 is that just money from employment? Also, please be aware that I had to provide my attorney with any bank account balance more than $1000 and provide all assets. I even went as far as to disclose cetrificates of deposits which was the building of my emergency fund when I started my plan to file. I was able to exempt these but $4000 and the trustee might want his share if not all of that, just something to be aware of.
See my reply on other thread. Please try to not double post as it may take some time for replies but we are all here to help.
Absolutely solid advice above! Don’t know what to add