An operation to separate conjoined Irish twins dubbed the "little fighters" is due to be completed.
Hassan and Hussein Benhaffaf's mother Angie said her baby boys needed "just one more miracle".
About 20 staff, including four anaesthetists and four surgeons, were working in shifts during the complex procedure which began at Great Ormond Street Hospital, in central London, on Wednesday.
The brothers, from east Cork in Ireland, were born in December at University College London Hospital.
In a poem, Mrs Benhaffaf said she and her husband Azzedine were told during the pregnancy the boys might share a heart. But their cries turned to tears of joy when "my little fighters were born" on December 2, she wrote.
The boys are joined at the chest but do not share any major organs.
Her poem said the twins had "fought to be here" and the operation to separate them was their "final battle".
The Benhaffafs relocated their entire family - including daughters Malika, four, and Iman, two - for the operation and recovery period and expect to remain in London for up to four months.
Mrs Benhaffaf said in her poem she would be grateful for the time the family had together, whatever the outcome of the operation.
"No matter how this will all end/ I am forever grateful for the time we did spend," she wrote. "Always remember, you are not alone/ Please God someday, we'll all return home/ I feel I must be one of the luckiest mums/ To have not one, but two precious sons."