MORE than 100 Sydney couples have volunteered to trial a male hormonal contraceptive since it was announced by doctors at the ANZAC Research Institute this month.

The willingness of men to take responsibility for contraception signals a shift in attitude towards family planning, from the onus being mainly on the woman to something shared between partners, experts say.

It also highlights a modern dilemma - the increasing concern of some men that a woman might trick them into a pregnancy, leaving them trapped in a relationship or with a responsibility they do not want.

The director of research at Family Planning NSW, Edith Weisberg, said that while such women were in the minority, some did deliberately become pregnant from a one-night stand or short-term fling.

"I've had a number of patients who were desperate to have a child but their body clock was running out, so they got into a relationship with the aim of getting pregnant," Dr Weisberg said.