A pregnant woman who arrived in British Columbia aboard the MV Sun Sea last month is the first of the nearly 500 Tamil migrants to be ordered released from detention.

The woman, whose name is protected by a publication ban, was ordered released by the Immigration and Refugee Board during a detention review in downtown Vancouver Monday.

Canada Border Services Agency argued for the woman's continued detention on the grounds of establishing her identity.

Since refugee board hearings began, CBSA has said it's prioritizing cases involving women and children.

But IRB adjudicator Michael McPhalen said the border agency's authentication efforts have not been reasonable, at least in this one case.

In ordering the woman's release, Mr. McPhalen said he can't imagine a case that was a higher priority.

The woman, who sailed on the MV Sun Sea with her husband and three other children, had a Sri Lankan national identification card that had been deemed authentic.

She requires treatment for an ongoing health issue and one of her children has a head wound.

Her husband is one of 380 men being jailed at a correctional centre in nearby Maple Ridge.

Melissa Anderson, an IRB spokeswoman, said the woman was not ordered to pay a bond. She must report to the CBSA office closest to where she resides by Sept. 16.