Develop after-sex contraceptive pill for routine use, urge researchers: Political opposition biggest hurdle

But the biggest hurdle impeding its development is likely to be political opposition, they suggest -- despite the fact that some current contraceptive methods, such as intrauterine devices (IUDs), can sometimes prevent pregnancy even after fertilisation.

There would be many advantages to routine "post-fertilisation" contraception -- as distinct from emergency contraception that has to be used within 72 hours -- write the US and Swedish specialists in reproductive health, public health, and economics.

For one, this method could be used for far longer after sex than emergency contraception, so would serve a much wider number of women than are currently able to access emergency contraception and use it within the defined time window.

It would also be more convenient, offering the potential to be used just once in the monthly menstrual cycle, no matter how many times a woman had had sex before taking it, or even when a period had just been missed.

"Importantly, post-fertilisation methods would eliminate the conceptual and logistical challenge of needing to obtain and initiate contraception before having sex, which can be daunting for both women and men," write the authors.

There would, of course, be technical hurdles to overcome, they acknowledge, as it's not clear whether some currently available drugs that can disrupt pregnancy either before or after implantation would work as effectively if used in this way.

But there are other promising compounds and the pharmaceutical know-how to develop them, confirm the authors. "Multidisciplinary research may be needed to define the best option, but given our rapidly increasing understanding of reproductive physiology, ultimate success seems likely," they say.

Political opposition is likely to pose a far greater challenge, they emphasise, as both the UK and US governments define the start of pregnancy as implantation of the fertilised egg, and interrupting this afterwards "is abortion by any definition," they write.

But abortion is legal in many countries and widely accepted by the public worldwide. And international data point to the greater safety of legal abortion the earlier it is carried out, they point out.

"Research from diverse settings has found that many women view medical abortion methods, particularly when used at home, as more natural and more compatible with their religious or ethical views than clinic or hospital based surgical procedures," they write.

Survey evidence suggests that women back the idea of post-fertilisation contraception; all that's lacking are "intrepid" funders who would be willing to kick-start the research, say the authors.

"To meet the challenges of our increasingly complicated world, women deserve all possible options for controlling and preserving their reproductive health and lives," they conclude.

In an accompanying podcast, lead author Elizabeth Raymond, senior medical associate at Gynuity Health Projects in New York, acknowledges the need to win over policy makers. Specialists working in family planning have their part to play, she suggests.

"We need to stop extolling pre-fertilisation contraception as a good thing, because it implies that something that works after fertilisation is bad. We have to stop doing that," she says.

"[Post-fertilisation] contraception doesn't have to be acceptable to every woman," she adds. "No method is acceptable to every woman now."