Transfem

Most of those risks were related to the old form of hormone therapy which had a high cancer risk, so they cut the recommended levels in half to compensate. Modern hormone replacement drugs don't have that risk anymore. Even the US FDA has removed their cancer warnings on estrogen therapy. Also, there has been some controversy on the research that gave those accepted levels, even for cis-women, having too small of a sample size and not at all diverse to take into account age, race, location, diet, etc. And there really isn't much research at all concerning levels during puberty, which is what mtf people are kind of trying to simulate in the first several years. And pregnant women are exposed to levels sometimes ten times as high as nonpregnant women, though admittedly for shorter periods of time.

The latest recommendations I originally found via Mount Sinai's site from my original hormone prescriber just for estrogen blood tests in general, but unfortunately they've broken the link.

https://www.mountsinai.org/health-library/tests/estradiol-blood-test

Here's a copy on way back machine. Though, without a lot of the content and links.

https://web.archive.org/web/20250126143445/https://www.mountsinai.org/health-library/tests/estradiol-blood-test

But this is the value they show as normal for all women including cis-women.

Female (premenopausal): 30 to 400 pg/mL (110 to 1468.4 pmol/L)

The other issue is that most of these risks are for post-menopausal cis-women. For example, in one major study, women who had a lifetime of higher estrogen levels showed 3% of them developed breast cancer in their lifetime than women who had lower levels. But that's not applicable to us.

There are 0 direct studies on how estrogen therapy affects trans-women, mostly just after the fact and very small sample sizes. There are some additional risks to estrogen overall though, such as bone density reduction, heart attack, stroke, etc., but things like heart attack and stroke are way, way more likely to happen with even normal cis-male levels of testosterone, and even more likely from anti-androgens. So, you should definitely discuss it with a professional. I chose to accept any small risk of higher estrogen levels but that meant never needing anti-androgens (may not work if you've already started anti-androgens, though according to some research), and to actually get the full effect of estrogen on my body, like having more feminine emotional reactions. Unfortunately, I didn't get much breast growth despite having a family with larger ones, lol. Probably because I was older when I started. But for me, with little personal medical issue history and the research my doctor had shared, her personal experience with HRT, and my own research reading many, many medical research journal articles wherever I could find them, it was well worth it. Again, YMMV, but the 100-200pg/mL recommendation is definitely out of date, and much of the rest of the research on risk is irrelevant to trans-women. There just isn't enough research on trans-women to say for sure, so doctors often stay conservative on levels.