The women were arrested last May and charged with crimes such as spying and undermining national security.
They had been campaigning for an end to the country's male guardianship system and for the right to drive, before the ban was lifted last June.Since then, horrific details have emerged of their alleged mistreatment at the hands of the Saudi authorities.
On Tuesday, Walid al-Hathloul, the brother of one of the best-known activists, Loujain al-Hathloul, told the BBC his sister was so traumatised by what had happened to her that she wanted to remain in jail, afraid of how her reputation had been unfairly smeared in her absence.
He said that following her arrest Ms Hathloul had been taken to a secret detention facility near the maximum security prison of Dhahban in Jeddah. There, she told her family, she was taken down to a basement and subjected to waterboarding and electrocution.
He named Saud al-Qahtani, a close confidant of the Saudi Crown Prince, as the man who oversaw her torture, allegedly laughing as he threatened to have her raped and murdered.
'Shrouded in secrecy'In February a group of British MPs carried out an investigation, supported by a number of international human rights organisations, into the allegations of mistreatment of Ms Hathloul and other female activists. They concluded that the allegations were credible.
In March the UN's Human Rights Council called for their release and more than 30 countries, including all 28 EU members, signed a statement condemning their prolonged detention.
The Saudi government says the detained women enjoy all the rights afforded to them under Saudi law.
But Mr Hathloul said everything about his sister's arrest and detention had been shrouded in secrecy and that the entire judicial process lacked transparency - it was not until November 2018, he said, six months after her arrest, that the family even learned what she was accused of.
The accusations, he said, included "applying for a job at the UN and being in contact with human rights organisations". He added that the prosecution had not produced any evidence to support its allegation of spying.
While Saudi Arabia rejects all criticism of its judicial system, insisting it is based on Shari'a (Islamic law), in practice it has always been opaque, with arbitrary judgements often handed down at the whim of a judge.
This case has attracted particularly widespread international condemnation and is seen as further damaging the reputation of Saudi Arabia's controversial Crown Prince Mohammed Bin Salman, known as MBS. Initially courted in the West as an enlightened reformer who has reintroduced cinemas and public entertainment to the conservative Kingdom, MBS remains under suspicion for his alleged involvement in last October's murder of the journalist Jamal al-Khashoggi, which his government denies.
Commentators have explained the apparent paradox between the accelerated crackdown on human rights and the Crown Prince's simultaneous liberalisation of Saudi society as being the ruling family's determination to steer reforms at their pace, rather than at the one demanded by peaceful protesters.
This, in a country where all political parties are banned, would be seen as a dangerous precedent.
What next for the activists?
The next stage expected in the trial of Loujain al-Hathloul and her co-defendants is the judge's response to their defence, which has already been submitted.
Her brother said the family were deeply worried about what would happen next, partly due to the lack of transparency.
He said his sister was bearing up despite everything, but that she was disheartened that the Saudi authorities had so far failed to investigate her complaints of torture.