In Luke 1:42, when the pregnant Mary visits her cousin Elizabeth, Elizabeth greets her by saying, “Blessed are you among women, and blessed is the fruit of your womb.” This verse, of course, later became part of the “Hail Mary” prayer.
Incidentally, the expression “fruit of thy womb” is also found elsewhere in the Bible, not just in reference to Jesus — in Deuteronomy 7:13 we read:
He will love and bless and multiply you; he will bless the fruit of your womb and the produce of your soil, your grain and wine and oil, the issue of your herds and the young of your flocks, in the land which he swore to your fathers he would give you.
When I consider this image, I like to think of Mary as being the tree/branch, and Jesus being the beautiful, life-giving creation that comes out of her. It’s a lovely way to think of pregnancy and birth.