The Zohar discusses the ability of Rachel to give birth to Binyamen, which came about through the spiritual level of Mazal. This spiritual realm is where all child-bearing originates.
Though it may be a person's destiny to be unable to bear children as a result of a prior incarnation, spiritual transformation of character gives one the power to rise above destiny - the stars and planets in the heavens-and experience the miracle of childbirth. We can reach this spiritual level, which lies above the plane of the planets, through the Light that shines in Rachel's soul. Our connection to the matriarch's soul is made through this passage and we can share her energy with people who are struggling to bear children.