The 34-year-old mother-to-be will have to give birth in May behind bars after being sentenced to 15 months’ jail at the Sydney District Court this morning. She will serve a minimum term of seven months.

When her supporters in court heard she was going to be sentenced to jail, several gasped and one woman doubled over and cried.

Judge Paul Lakatos said it was a “sad result” she would have her first baby in custody and wished her a “successful” pregnancy.

The woman pleaded guilty to five counts of sexual intercourse with a person under her care over three months in 2016 while she worked at the elite Sydney Grammar School.

The father of her baby is her husband, not the teenage boy.

She cannot be named to protect the identity of the victim, who was 17 when she began to abuse him. The pair began to meet in relation to a school activity but their text messages soon became emotionally charged.

“The nature of the interaction changed between them,” Judge Paul Lakatos said.

The teacher performed oral sex on the student on school grounds and in a store room as well as in her home. Their relationship turned sexual after she showered him with gifts, including books of poetry, and told him personal details of her life, including problems in her relationship with her husband.

The court heard “she made him write sex fantasies for her and they exchanged sexual fantasies”.

Judge Lakatos said the ex-teacher had no criminal history and was a “high achieving, well regarded” teacher “which in itself is a tragedy”.

He said it was “difficult and unpalatable for judges and magistrates to impose jail for the first time ... But in my view I consider no other alternative to full custodial term.

“It was her duty to care for her student’s welfare and exercise proper regard for his welfare in circumstances where he could not.”

He said the jail term would be “onerous” due to her pregnancy, the nature of her offending and her mental health issues.

The teacher met the 17-year-old victim at her home, a classroom and a school storage cupboard as they embarked on what she thought was a “very mutual love affair”.

She also wrote in a report to his parents that the boy was “a delight to teach”.

The then-teacher bombarded the student with text messages for months after he ended their sexual relationship, apologising, telling him she loved him and referring to herself as a “f***ing monster”.

One extraordinary message was sent on behalf of her dog, who “would like to say hello and ask how you are”.

The message read: “He knows it’s over between us, but he still cares about you. He hopes you won’t stay angry too long and that maybe we can talk before school goes back.”

In his victim impact statement, the victim said he felt harassed and stalked and “didn’t feel safe at school”.

He said the ex-teacher was “domineering” and he felt “overwhelmed” by her advances. Despite her emotional blackmail” he tried to end the relationship a number of times

According to a pre-sentence report, the former teacher later said she knew the relationship wasn’t appropriate but “it felt right”. However, she admitted to feeling “shame and remorse” about the “damage she’d done”.

She had already been the subject of several complaints and had been reprimanded over her conduct with other male students.

“If all boys had his sense of humour and level of engagement with the world around them, then teachers would skip to school,” the teacher wrote in the school report.

Prosecutors this week sought a jail term for the woman, despite her being pregnant.

The police facts state the relationship continued despite the victim being “scared to end the sexual ­relationship with the offender because he ... was worried she would self-harm”.

They continued: “He repeatedly said to her, ‘I can’t’ ... The offender responded to the complainant in a dismissive way saying, ‘what do you mean you can’t?’”

The teen finally ended the relationship in April but the teacher continued to contact him.

He attempted suicide in the school toilets at the end of 2016. Judge Lakatos said he accepted the victim believed the offending led to the attempt on his own life, but there was no medical evidence before the court “that was the cause”.

Text messages in the facts revealed the teacher described herself as a “f***ing monster” to the student. When the teacher found out a friend of the victim knew about the relationship, she asked, “Am I going to jail?”

The student replied: “No, you’re not.”

The ex-teacher will be eligible for parole on September 1.

If you or someone you know needs help, please contact Lifeline on 13 11 14

Additional reporting: AAP

andrew.koubaridis@news.com.au