Utah officials on Monday filed a brief arguing that allowing gay and lesbian couples to marry would lead to fewer children.

More than 1,300 gay couples married following a federal judge's December 20 ruling declaring invalid Amendment 3, the state's 2004 voter-approved constitutional amendment limiting marriage to heterosexual unions. The state appealed the ruling to the 10th Circuit Court of Appeals in Denver, which will also review an appeal from the state of Oklahoma involving a similar ban.

In its 120-page brief, the state argues that marriage is “principally a child-centered institution, one focused first and foremost on the welfare of children rather than the emotional interests of adults.”

Allowing gay couples to marry would “tend to encourage more parents to raise their existing biological children without the other biological parent.” It would also “over time weaken [Utah's] marriage tradition enough to reduce its fertility rate, perhaps even below the replacement rate.”

Legalizing same-sex marriage would also increase the state's divorce rate, the brief claims.

Oral arguments in the case are scheduled for April 20.