What do you think of borrowing money from my 401k to pay for IVF?
Please give me some advice.

Thanks!

It all depends on your finances as a whole, your home equity, your job security, and any other assets.
If your 401K is your only asset to borrow against, I would wait, if you are young enough.
(I'm assuming you have no savings.)
If you need to borrow to have a child, will you be able to pay it back when raising the child?
You will be SO glad you have those tax free amounts in your 401K when you are 59 1/2! (Not trying to make your wish to have a child sound unimportant.. )

It depends on how quickly you can pay it back. The issue here is that if the IVF succeeds, then you may be leaving the company. Even if you don't, your pay will stop and the loan will not be able to be repaid. If that happens, the loan becomes a withdrawal with all the penalties inherent in a withdrawal.