The purpose according to the Holy See is to “thank the Lord for his total self-giving to the world and for his Incarnation which gave every human life its real worth and dignity,” and to “invoke the Lord's protection over every human being called into existence.”
It can, I think, safely be assumed that, leading on from this general intention, the Pope envisaged that the prayers themselves should refer specifically to such examples of nascent life as the human embryo, and the child in the womb.
Here, in magnificent response, are the US Bishops’ worship resources for prayers of supplication, most helpfully linked from the E&W Bishops’ site:
Supplications for Vigil for All Nascent Human Life
Let us pray to God, the Father of Life and Font of all Mercy:
Lord, have mercy on all who have sinned against life.
You knit us in our mother’s womb,
— Preserve all children from bodily harm
From the moment of conception.
Your Son ennobled all human life when he became flesh in the womb of the Virgin Mary,
— Enlighten our minds to see the dignity of every human life
From its earliest embryonic beginnings.
You are author of science and knowledge,
— Bring an end to the destruction of human embryos
In research facilities and IVF clinics.
You are the law-giver and ruler of the world,
— Help us to overturn unjust laws that permit the destruction of innocent lives,
And guide our public officials to defend the littlest among us.
You love those who are afflicted,
— Help parents of unborn children with disabilities
To cherish the baby you have entrusted to their care.
Your Son, Jesus, healed the sick,
— Guide all doctors to be guardians of life,
Especially the lives of unborn children with serious health conditions.
Lord, you are love and mercy itself,
— Draw all who have acted against innocent human life
To repentance and forgiveness,
And heal them through an outpouring of grace.
The US Bishops’ prayers, beautiful and comprehensive as they are, have been composed for a vigil service, and might need some trimming for use in the bidding prayers at parish Masses. I mention this because the English Diocese of Clifton has announced its own plan for the day: an hour of quiet vigil in the cathedral before the 6.00 pm Mass, and a bidding prayer at every parish Mass that weekend.
A vigil of quiet prayer will be held in the Cathedral at 5.00 pm on Saturday, before the celebration of the First Mass of Sunday.
Bishop Declan has written to all our parishes. He said: “I would like to ask you to include the following prayer in your intercessions at Masses that weekend:
‘In union with the Holy Father we thank the Lord for his total self-giving to the world and for his Incarnation which gave every human life its real worth and dignity. Let us ask the Lord's protection over every human being called into existence. Lord hear us.’”
This is, just about word for word, the Holy Father’s general intention. Since Bishop Lang has omitted any specific reference to nascent human life, which is after all what the day is about, I very much hope that the clergy of the individual parishes will insert their own references to it.
Update, Sunday 28th November: The bidding prayer was included at the Mass I attended, using the exact wording requested by the Bishop. No explanation or context was given. There was no mention of nascent life, the embryo, the unborn child, or the child in the womb. There has been no mention of the day of prayer in the weekly newsletter, either last Sunday or this.