Hi, trans woman here!

There are two aspects that affect fertility specifically for trans people:

• hormone treatment (HRT) involves replacing the body's endogenous sex hormones with those of the desired sex.
• "the surgery" or bottom surgery, which in most cases involves removal of the testies or ovaries/uterus, in addition to possible construction of desired genitalia.

The fact is most trans people don't have access to surgery. It's too expensive, or there are other concerns like not receiving support from doctors or therapists. Some people are simply afraid of the risks or undesirable results, which are very real as with any surgery. But it will put a final end to reproductive capacity. For now. Some of us hope one day science and technology will allow eg trans woman to conceive and carry a pregnancy.

HRT is far more accessible, and from a younger age, maybe 16 for puberty-blockers with parental consent in some areas -- but this is the exception. Most trans people can't get HRT until they are 18 and really I would say it's more common later in life. The 20s-30s can be a particularly distressing time (sex characteristics become even more defined) when trans people find motivation and means to medically transition. But this leaves time to have children, I know many trans people who had children before transitioning.

HRT obviously will put an end to reproductive capacity, at least while taking it, and in fact may become permanent. It's not unheard of for trans people to pause hormone therapy in order to attempt conceiving with their partner. Sometimes it works.

A better option would be freezing sperm, or I presume eggs, before starting medical transition. It's an expensive process, and so again not affordable to many trans people regardless of their desire for children.

It should also be stated that regardless of desire for children, quite a few trans people choose to not transition, for social, career, or personal reasons. Children and marriage are a commonly given reason I've seen.

I guess the Vatican and far-right don't know this, or maybe they do and pretend not to understand, although knowledge is something both claim to value. Then again I never considered the Catholic church to be experts on any sexual matters. They are usually centuries behind what science discovers in all fields. It turns out the bible isn't a great reference book for the human endocrine system.

The best option is not only improved access to gender-affirming care (this makes trans folks happier), less discrimination and scapegoating, but also increased education about and funding for preserving fertility. Being trans doesn't have to mean being childless.