The North Dakota legislature passed a bill that defines life as beginning at conception.
The law is another move towards outlawing abortion in the state by the Republican-controlled House.
The bill was passed 57-35 and will now be sent to the Republican governor, Jack Dalrymple, who has not said whether he will veto the bill.
The North Dakota Senate already passed the bill last month.
The new law outlines what is known as the "personhood measure" which essentially gives rights to egg.
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Critics say the bill is unconstitutional and violates the Supreme Court decision of Roe v. Wade.
Roe v. Wade ruled that abortion was legal until the fetus was considered viable - namely, that the baby could live outside the womb.
North Dakota has one sole abortion clinic in Fargo but recent laws have threatened it with closure, including a bill that bans abortions after 20 weeks of pregnancy
Another bill passed by North Dakota lawmakers requires a doctor with hospital-admitting privileges to perform abortions.