Swiss voters are set to decide whether to allow same-sex couples to wed and adopt children after a highly charged campaign pitted gay rights activists against traditionalists in one of the last Western European countries to still ban gay marriage.
The vote will be held on Sunday.
The federal government and parliament have approved opening civil marriage to same-sex couples, but opponents forced a referendum on the issue under Switzerland's system of direct democracy.
In a provocative campaign, opponents of the reform used images of crying babies and the word "slaves" written over dark-skinned pregnant bellies, in a reference to surrogacy that is illegal in Switzerland, in stark contrast to proponents waving "Yes, I do" rainbow flags at Zurich and Geneva pride parades.
Showing the no-campaign in the traditionally conservative and Christian Switzerland had gained traction in recent weeks, the share of voters set to approve same-sex marriage fell to 63 per cent in the latest poll by gfs.bern for broadcaster SRG, while the share of opponents rose to 35 per cent, versus 69 per cent to 29 per cent a month earlier.
In Switzerland, same-sex couples received the right to enter civil partnerships, but not marriages, in 2007 and the right to adopt children parented by their partner in 2018.
Under the amended law, both male and female same-sex couples would be allowed to adopt children unrelated to them in the same way as their heterosexual counterparts.
Married lesbian couples would also be allowed to have children through sperm donation, which is currently legal only for married heterosexual couples. Under the law, both women would be recognised as the child's official parents from birth.
Antonia Hauswirth of the national committee "Marriage for All" told Reuters the current adoption procedure could take three years. "If something happens to the biological mother during this time, the child is considered an orphan."
The proposed scheme would give children born from a sperm donation two parents from birth and thus better legal protection, she said.
Opponents say the changes would deprive children of a father.
"Tomorrow, a child in Switzerland will still have a mother, but just an 'other parent' instead of a father. The father just gets deleted from the civil code, that's not acceptable to me," Olivier Dehaudt, member of a referendum committee objecting to the proposal, told Reuters.
The proposed legal change would also open an easier path to citizenship for the foreign spouse of a Swiss citizen.