Tim asks on the Open Theist facebook page:

Of all the verses in the Old Testament, I have struggled with a question on this one verse, Psalm 139:16.
Here it is in the New King James (NKJV)
Your eyes saw my substance, being yet unformed.
And in your book they all were written,
The days fashioned for me,
When as yet there were none of them.

Now, to be honest, the Hebrew is difficult, but is there a
Calvinism in this translation? Or how does one explain this
verse if indeed it says all the psalmist’s days were
written before he was born?

An article by Boyd was posted in response, reading:

The Jewish Publication Society (JPS) translation in essence agrees with the KJV. It reads:

“Your eyes saw my unformed limbs;
they were all recorded in Your book;
in due time they were formed,
to the very last one of them.
How weighty Your thoughts seem to me, O God.”

So the Hebrew is obviously sufficiently ambiguous to allow experts to disagree on what was pre-recorded in God’s “book”. The issue of whether David’s “days” or “unformed limbs” were pre-recorded in God’s “book” must thus be settled on other grounds, the most important of which is the immediate context of the passage.

Given that this whole passage is about God’s intimate knowledge of David when he’s growing in the womb — not about God’s foreknowledge of David’s life — it seems much more reasonable to favor the translation that has God pre-recording David’s body parts. If so, David is simply expressing God’s loving care in making sure all that’s supposed to eventually be part of David’s body is in fact being formed in the womb. (By the way, it’s important to remember that we’re reading poetry here. It’s thus a mistake to try to draw out metaphysical conclusions about what this implies for babies who are born with body parts missing or deformed.)”