How do you know? I mean, it's not like HN profiles have mandatory gender field, and there are higher-ranked profiles than yours that don't link to external profiles or provide real names from which (risky) guesses can easily be made about gender, and whose comment/post history doesn't, on a quick review, give any direct indication of the user's gender.
http://micheleincalifornia.blogspot.com/2015/01/some-raw-dat...
I usually couch it in terms of "I appear to be the highest ranked openly female member here" because, no, there is no absolute way to know. But I have also been saying that for something over two years and, so far, no one has jumped up and said "Nope! HERE is a link to HNmembername who is openly female and outranks you!" Given that this is HN, I consider that fact to be probably strong evidence that no one knows of any openly female members who outrank me.
Of course, this does not preclude the possibility that there is a woman with more karma who is actively hiding her gender. But even if there is, that still makes my typical framing -- apparently highest ranked openly female member -- an accurate statement.
Edit: Just as an FYI, I upvoted you. It is a perfectly reasonable question to ask and the framing is perfectly reasonable. I don't know why people are downvoting you. That sucks. Meanwhile, some other comment that is being genuinely dismissive of me and the pertinence of my "rank" here is being upvoted. And that sucks even more.