Sudan is facing growing condemnation for sentencing a pregnant woman to be whipped and then hanged for adultery
Governments, the UN and human rights groups are also concerned that she is being kept shackled in prison with her toddler son a month before she is due to give birth.
They have called on the Sudanese government to immediately release Meriam Yahya Ibrahim, 27, and overturn both her death sentence and sentence of 100 lashes. More than 100,000 people have backed a call by Amnesty International to release Ibrahim.
Ibrahim was arrested after a Muslim relative claimed her marriage to a US citizen was invalid, and therefore adulterous, because he is a Christian. Ibrahim was also found guilty of apostasy. But she said she was brought up a Christian and refused to renounce her faith.
Her lawyers have lodged an appeal against the sentence, which may be heard in Khartoum this week.
Ibrahim is being held in harsh conditions and is constantly shackled, according to Amnesty. Her 20-month-old son, Martin, has been kept in prison with her since February.
Ibrahim has been told that her execution will be deferred for two years to allow her to deliver and then wean her baby.
Her husband, Daniel Wani, who left Sudan for the US in 1998, has travelled to Khartoum to try to secure the release of his wife and son.
He said Ibrahim was being denied medical treatment and he had not been allowed to visit her or Martin.
The Sudanese authorities have reportedly refused to release the child to his father's care because of his Christian faith.
Ibrahim - a graduate of Sudan University's school of medicine - told the court she was the daughter of a Sudanese Muslim father and an Ethiopian Christian mother, but was raised as a Christian after her father left the family when she was six.
According to Human Rights Watch, article 126 of Sudan's criminal code says a Muslim who renounces Islam is guilty of apostasy, punishable by death, unless the accused recants within three days. The UK government has summoned Sudan's diplomat in London to the Foreign Office to hear its "deep concern".
Foreign Office minister Mark Simmonds said: "This barbaric sentence highlights the stark divide between the practices of the Sudanese courts and the country's international human rights obligations."
US State Department spokeswoman Jen Psaki said the US was "deeply disturbed" by the case.
The Canadian and Dutch governments have also expressed concern.
The UN has also urged Sudan to adhere to international law. "We are concerned about the physical and mental wellbeing of Ms Ibrahim, who is in her eighth month of pregnancy, and also of her 20-month-old son, who is detained with her at the Omdurman women's prison near Khartoum, reportedly in harsh conditions," said Rupert Colville of the UN Human Rights Office in Geneva.
Amnesty said: "The fact that a woman has been sentenced to death for her religious choice, and to flogging for being married to a man of an allegedly different religion, is appalling and abhorrent."
Wani became a US citizen in 2005. He and Ibrahim met in Khartoum and were married there in 2012.
Wani had taken steps to take Ibrahim to the US.