Craig Jaret Hutchinson of Nova Scotia was afraid his girlfriend of nine or 10 months intended to leave him, so he poked pin-sized holes in condoms and got her pregnant. On Friday, the Supreme Court of Canada will decide whether his deception constituted sexual assault, in a case that could alter the definition of consent.

The case pits concerns about women's autonomy and right to say no against fears that sexual assault would be trivialized if deceptions are seen to nullify consent. The Supreme Court touched on that fear in cases involving men and women who did not inform their partners they were HIV-positive, ruling that there is no true consent where one partner keeps another in the dark about "a significant risk of serious bodily harm." (If those with HIV can show they have a "low viral load" and use a condom, they do not need to inform their partner.) But the Hutchinson case does not involve such a risk, according to lawyer Luke Craggs, who is representing Mr. Hutchinson.

"Are we criminalizing deception without the risk of bodily harm?" he asked in an interview. Doing so "has the potential to criminalize anyone who lies about any part of a sexual act, so if a woman lies about being on the Pill, that's potentially sexual assault."

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Chris Levy, who teaches law at the University of Calgary, says the key question is what is a relationship problem, and merely private, and what should be dealt with by the criminal law. "Where do we draw the line and how we draw it?" He gave his first-year class an exam question last year based on the case, in which a hypothetical woman goes on the Pill and cheats on her partner, who had been led to believe they were trying to start a family, and who then goes to the police. (The students were "all over the map," but some men were "agitated because they were the ones who had been tricked.")

The case has been before the courts since 2007, after a distraught Mr. Hutchinson sent texts admitting the deception to his girlfriend after she broke up with him. She had an abortion, and endured two weeks of bleeding, blood clots, severe pain and a serious infection. Mr. Hutchinson was acquitted at his first trial, but when the Nova Scotia Court of Appeal threw out that ruling and sent it back for a second trial, he was found guilty, and sentenced to 18 months in jail. The appeal court upheld that ruling by a 4-1 count, with the dissenting judge warning of women being charged for lying about being on the Pill. (Judge David Farrar, the dissenter, said the Nova Scotia government had conceded that point about women being charged for lying about the Pill.)

The government did not directly concede it in its written argument filed with the Supreme Court. Because Mr. Hutchinson's deception was not about "the motivation for the sexual act" – which could include lies about wealth or position – but was a "deception regarding the physical sexual act," finding him guilty would not lead to charges in circumstances that could trivialize sex assault, it said.

It argued that the woman, whose name is protected by a publication ban, consented only to condom-protected sex, because she did not want to become pregnant. "Having control over who touches one's body, and how, is at the core of human dignity and autonomy."

Hilla Kerner, a worker at the Vancouver Rape Relief and Women's Shelter, said deceiving women about condom protection should be seen as a sexual assault because it is a denial of informed consent. "There is a difference between jeopardizing women's physical health and other situations." Of women tricking men about being on the Pill, she said, "it's such a stretch. We're not in a crisis of sexual assault and deceitful rape, from women to men."