Superior Court Judge Al Girolami said releasing the information could hamper the murder investigation and prejudice public opinion before a trial begins.
Girolami is scheduled to hear more arguments June 6 from prosecutors preparing a murder case against Peterson's husband, Scott Peterson. Prosecutors on Thursday asked that the autopsy reports be released to the public. They argued that media leaks of the reports are biased toward the defense.
Girolami also ordered that leaks of sealed information stop and indicated he would consider a gag order to stop the prosecution and defense teams from talking to the media.
Scott Peterson, 30, is accused of killing his wife and unborn son, whom the couple had planned to name Conner, last December in their home. Laci, 27, was eight months pregnant at the time. The bodies washed ashore in San Francisco Bay last month.
Contra Costa County authorities concluded their autopsy report earlier this month, but did not disclose the cause of death.
Several media outlets have released details of the coroner's report, and a spokeswoman for Laci Peterson's family members said Thursday they were "devastated" at hearing autopsy reports without warning on television.
The leaked reports indicated the unborn son had plastic tape wrapped around his neck and a significant cut across the shoulders.
Meanwhile, friends of Laci Peterson removed several personal articles from the single-story Modesto home Friday where she and Scott Peterson lived. Peterson's defense lawyer, Mark Geragos, said he had worked out arrangements earlier this week for family members to go into the house to remove items.
But the gatherers, who included Laci Peterson's brother, Brent Rocha, set off the home's alarm when they arrived without notice. They dispersed quickly when media crews arrived, driving off with a rocking chair and numerous other belongings.