A woman and the boyfriend of the pregnant Alsip teenager found strangled in a south suburban forest preserve were charged with first-degree murder Thursday in the death of Rosemary Newman, authorities said.

Deandre Minkens, 20, of the 300 block of 156th Place in Calumet City, and Shante Thomas, 19, of the 14500 block of Woodlawn Avenue in Dolton, also were charged with intentional homicide of an unborn child, a spokesman for the Cook County state’s attorney’s office said.

Authorities said that Minkens and Thomas spent several weeks planning to kill Newman, 18. Minkens invited Newman to a Crestwood restaurant Saturday, having Thomas hide in Minkens’ vehicle while he and Newman ate, sheriff’s officials said in a news release.

As Minkens drove from the restaurant, Thomas emerged from the rear of the vehicle and began choking Newman, authorities said.

Both defendants then beat Newman until she lost consciousness, authorities said. Minkens then drove to a Cook County Forest Preserve near Calumet City, where he strangled Newman and dumped her body in the wooded area, authorities said.

According to her family, Newman was nine months pregnant and Minkens was the father, but he denied paternity.

Minkens and Thomas are due in bond court in Markham on Friday morning.

Newman’s mother reported her missing Sunday morning, a few hours after a man walking his dog near Freeland Avenue and Warren Street discovered the woman’s body about 15 miles from her home, Alsip police said.

Rosemary Newman’s brother, Michael Newman, told the Tribune his sister left for a date with Minkens on Saturday night and that was the last time her family saw her.

For weeks, her boyfriend hadn’t called her, and he denied her child was his, Michael Newman said. Rosemary planned to have a DNA test done once the baby was born, he said.

On Saturday, Minkens called and texted Rosemary, inviting her to dinner at Applebee’s, the girl’s brother said.

Although her mother and brother urged her to stay at home, Rosemary showered, dressed, and scribbled a message on a piece of paper that read “”he already in my hands because he want to get back with me,”” Michael Newman said.

She left the house around 10:30 p.m. and later called her mother from the restaurant, her brother said.

She never returned home.