There are 184 bishops or cardinals with voting rights taking part nearly two-thirds of whom come from the Pan-Amazon region, which covers nine Latin American countries.
The meeting, which ends Sunday, has also been attended by non-voting observers, auditors and experts, including 35 women.
Ecuadorian nun Ines Azucena Zambrano Jara said Friday a letter had been sent to the pontiff.
She told journalists at a press briefing that the women took an active part in the synod, with some of them defining themselves as “synod mothers”.
Specialized site Religion Digital said the 35 women had signed a petition calling for the right to vote.