Mexico's Supreme Court on Thursday ruled that a state law defining life as beginning at conception and equating abortion with murder was unconstitutional in another victory for abortion rights campaigners.
The unanimous decision by the top court concerns the penal code of the northern state of Sinaloa, but will also affect other states with similar laws.
"It's not up to any local legislature or this plenary to establish the origin of human life, especially in the absence of scientific consensus," said Judge Alfredo Gutierrez Ortiz Mena.
After Mexico City decriminalized abortion in the first 12 weeks in 2007, at least 10 of the country's 32 states passed laws obliging the authorities to protect life from the moment of conception.
The legislation meant that abortion was equated with infanticide, according to experts.
Mexico has a federated system in which the states establish their own laws, but they can be overridden by Supreme Court rulings that establish jurisprudence.
On Tuesday the top court ruled that women should not be punished for abortion, opening the way for women across the country to access the procedure without fear of being prosecuted and potentially imprisoned.
Up to now, abortion has been legal in four states including Mexico City in the first 12 weeks, while elsewhere, it was permitted in cases of rape.