One aspect of transmen getting pregnant that that's a huge concern is that we don't yet understand is how testosterone will affect the baby.
Until research shows that testosterone doesn't harm the baby then the media celebration of trans men who get pregnant is in very poor taste.
Obviously trans men stop taking testosterone when trying to conceive, but there's plenty of evidence to suggest that having taken these experimental hormones in the past can still cause harm to the baby many years later.
In the tragic cases of the East European Olympic female athletes who were given testosterone to boost their performance, many had children with life-limiting abnormalities. Even ten or fifteen years later the testosterone these girls had taken for a short time still affected their bodies in unpredictable ways.