How does that constitute the difference from being non-human to being human?

It doesn't. But one person's rights can be curtailed when they interfere with another person's rights.

You needing a kidney and my being a match doesn't mean I *have* to give one to you since that'd be a significant risk and/or strain on my own life. This is true even if you die.

Ditto Pregnancy, even if nothing goes wrong, is a very significant strain on the women's health and well being