New Jersey is changing its birth certificates to include a third non-binary gender category from February 1.
It is the fourth state in the US to introduce gender neutral birth certificates after California, Oregon and Washington all made the change.
From next month, parents in the state will be able to choose non-binary as their child's gender designation in addition to the traditional male and female categories.
The new regulation is named after New Jersey resident Babs Siperstein, the first elected transgender member of the Democratic National Committee in 2012.
The Babs Siperstein Bill also drops the requirement for transgender people to prove they have had gender reassignment surgery before being able to change their gender.
The new legislation was signed last July by New Jersey's Democrat Governor Phil Murphy, who said at the time: 'Today is an important day for New Jersey as we continue to strive toward equality for all of our residents, regardless of sex or gender expression.
'Allowing vital records to match gender identity is an important step forward that will allow transgender individuals to control the disclosure of their transgender status.'
Ashley Chiappano, of Garden State Equality, told News12 New Jersey: 'Just because your sex assigned at birth is one thing, it does not necessarily mean that it is something that's going to be consistent with your gender identity throughout your life.
'Sex is more like a label. When we're talking about sex, this is assignment by a doctor.
'Gender identity goes even further to say that it's how you feel on the inside and how you express yourself.
'It's how you express yourself through your clothing, your behavior, your personal appearance.'
At the start of the year, New York City changed the gender options on its identity cards to include a third 'X' option and also removed the need for a doctor's affidavit.
Daniel Moody, a Christian philosopher and the author of The Flesh Made Word, criticised the changes, telling The Christian Post: 'The new possibility has nothing to do with biology and everything to do with a destructive anti-body ideology. Anybody can self-identify their way out of the categories of male and female.'
He added: 'We can expect 'X' to quickly fragment and the list of specific identity options to grow longer, becoming even more meaningless.'