Thanks for checking out GRUNT and for reaching out to us. You have asked a very good question indeed.
There isn’t much in the way of formal resources or research that focus on reproductive health for trans men who have receptive sex with cis men. Indeed, as with many other communities, we learn about risk and experience from discussing it with each other while continuing to advocate and demand that our population of men be included in critical areas of research such as sexual and reproductive health.
We know that the use of testosterone for medical transition is not 100% effective in preventing pregnancy, however, the chances of a man who uses testosterone and who has also ceased menses for 6+ months falling pregnant is very slim, perhaps as likely as a cis woman taking birth control pills falling pregnant – not 100%.
Progesterone only (non-estrogen) biomedical methods include: implant (Implanon or Nexplanon), hormonal IUDs (Mirena, Skyla, and Liletta), the shot (Depo Provera) and even some kinds of birth control pills.
At the end of the day though, it’s always important to talk through reproductive health questions and concerns with your GP. Even if it’s awkward and you’re worried they might not know the answer, it is well and truly their job to find out.