Naomi Tekea Craig, 33, was last month charged with multiple offences including two counts of sexual penetration of a child over 13 and under 16.
From Mandurah, south of Perth, she has since been charged with three more offences police allege took place between 2024 and 2025.
Western Australian Police Commissioner Col Blanch on Wednesday confirmed a DNA test had been conducted after Craig gave birth.
Asked if the victim was the father, he said: "I believe so."
"I must be very careful, the matter is before the court," Mr Blanch said.
"More generally, it is a very serious and heinous offence."
The commissioner said the community should be shocked by any allegations involving young people being preyed upon.
"If it is by a person in the position of authority or care of another, it is even more aggravating," he said.
WA Police previously said Craig engaged in persistent sexual conduct with a male youth between 2024 and 2025.
"At the time of the commencement of the alleged offending, the woman was a teacher at a school in the Mandurah District, and the male youth was a student," a spokesman said.
Craig is scheduled to appear in the Mandurah Magistrates Court on Tuesday.
1800 RESPECT (1800 737 732)
National Sexual Abuse and Redress Support Service 1800 211 028
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