John Gill Commentary Genesis 35:17

"And it came to pass, when she was in hard labor, that the midwife said unto her, Fear not; for now thou shalt have another son." — Genesis 35:17 (ASV)

And it came to pass, when she was in hard labour
In the midst of it, and at the worst: that the midwife said to her, fear not ;
Since Rachel was big with child, it was necessary to take a midwife with them in the journey; and perhaps this might be one that was always kept in the family, and had been assisting to all Jacob's wives and concubines at their labours; and this seems probable from what follows, since she not only bids her be of good courage and not fear, comforting her under her pains, giving her hopes they would soon be over, and that she would have a safe delivery and do well: but she assures her of this, you shall have this son also ;
as she had one before, at whose birth she said, "the Lord shall add to me another son"; and therefore called his name Joseph, (Genesis 30:24) ; this the midwife remembered, and endeavours to comfort her with the accomplishment of it.