What do you say to someone who will probably lose their baby?

"I'm so sorry for your loss -- I can't imagine what you must be going through right now."

At this moment in their lives, you're going to offer far more comfort to them by LISTENING than by talking.

Torah and the Tenach has much to say about children. First, they are a blessing. I'm sure this couple knows that already. As far as the story of Dawid and Batsheva, the death of their child was a result of their sin. (The child was actually a product of their sin). I would not mention this one, unless you (or your friend) is certain that sin is not the cause of this early death. Job is probably the best bet because it seemed like a completely unfair situation. After all, no sins are mentioned as the cause for such death and destruction. However, the main thing is that Job remained faithful to Yahweh. Don't forget also Yahweh is a God of restoration! Job was given more children as a blessing! Although, a different child cannot take the place of the child lost it is a blessing to have another child just the same! Even if Yahweh does not save that child or give them another, He is still a Healer and can heal and even strengthen their marriage during this time. Life is never promised us. Whatever gift (even if it is a person) is given to us by Yahweh is His to begin with. Whether He lets us keep it or not, He is still a holy and loving GOd. Also don't forget that God also enters our griefs. Many times in the Old Testament, we see God's grieving over the destructions that have happened to His people. However, "though weeping may endure for the night, joy comes in the morning".

I agree with those saying the few words the better, and listening is the best idea right now. Right now though, I'd offer prayers up quite often, that none of this is necessary, like you say.

To give you something from the OT though, one of the great comforting Psalms is Psalms 139, God knows that child right now as it's in her womb, and knows it's days. Knows whether it's going to be born or go directly to Heaven. That would probably be a huge comfort to me if I were in the situation, but the pain would still be very difficult. God bless...

The Old Testament is Christianities version of Judaism.

Seek out a Torah or Talmud if you want Jewish verses.

But it is likely, at this time, they they are not looking for answers in the Torah. They are looking for comfort and support, which anyone can provide.

I think a sincere "I'm so sorry" would do fine. If it were me, I wouldn't want anything else said. He might say something that might make her really upset (on accident of course, not intentionally).

The child shall live and not die and declare the works of the Lord. Tell him to speak life over the baby.

unless you have been there, there is not much you can say apart from so sorry. the best is to "be" there for them, let them do the talking, we need someone to listen while we talk it out. it will take time. give it to them.