Psalm 139:13–16 describes the formation of a child in terms that make no category for accidental: "thou hast covered me in my mother's womb... my substance was not hid from thee, when I was made in secret... in thy book all my members were written, which in continuance were fashioned, when as yet there was none of them." The Hebrew word for "covered" — cakak — means to weave, to knit, to form intricately. Each child is described as a deliberate, specifically fashioned work. Unplanned to the parent does not mean unplanned to God.
Jeremiah 1:5 speaks to the specific child: "Before I formed thee in the belly I knew thee; and before thou camest forth out of the womb I sanctified thee." God's knowing of the person preceded their formation. The pregnancy that was a surprise to the parents was not a surprise to the one who formed the child in secret.
Commentary is from a charismatic Protestant perspective, drawing on KJV text and public-domain sources including Spurgeon, Andrew Murray, and Matthew Henry.