Bridgett Szychulski, a well-liked high school band director in Bucks County, Pennsylvania, is charged with having sex with a 14-year-old student in 2012.
She taught at Lenape Middle School in Doylestown, Pa., at the time.
Szychulski, 31, is married with a four-year-old son and pregnant.
Her hands cuffed in front of her expanding belly in court, she was arraigned on charges of involuntary deviate sexual intercourse earlier this week.
She also faces criminal counts of statutory sexual assault, aggravated indecent assault and indecent assault, and has been suspended without pay.
Szychulski was released on $500,000 bail pending trial.
Authorities launched an investigation into her conduct earlier this month after someone made an anonymous call to the state child abuse hotline.