Proverbs 3:5–6 commands trust that extends specifically to what we do not understand: "Trust in the LORD with all thine heart; and lean not unto thine own understanding." The Hebrew binah — understanding — is intellectual comprehension, the ability to make sense of something. Failed fertility treatment produces the specific anguish of a body that will not be understood or managed. Leaning not on your own understanding is hardest precisely when the understanding you most want — a medical explanation, a successful outcome — has not come.
Romans 8:26 offers a promise specifically for the exhausted who do not know what to pray: "the Spirit itself maketh intercession for us with groanings which cannot be uttered." The Greek stenagmois alaletois — unutterable groanings — describes prayer that has gone past words. After multiple failed cycles, some grief cannot be articulated. The Spirit prays it anyway. The failure of language before God is not the failure of prayer.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.