My daughter wants to know, how do doctors know whether a baby with Sirenomelia (Mermaid Syndrome) is a boy or a girl?

My guess is that they could check the fetus’ innards with xray.

Autopsy. Which is usually easy to perform, seeing as most Sirenomelia cases are stillborn, and most who are born die quickly.

Also from that article, many of the famous and surviving cases fail to really have functional genitals at all (One of the oldest known survivors, Shiloh Pepin, was born without a vagina).

Thank you @ragingloli

That was what prompted the question. Nice, @aphilotus! We just finished watching the show on her last 6 months of life.

I was thinking they probably did blood tests, but didn’t want to tell her for sure until I explored a bit.

A DNA test? The child would either have XX or XY chromosomes.
EDIT: I should have read your post above mine, yes a DNA blood test would be the most likely option.

Did she die?

@Nightmare She died earlier this year, but was old enough at the time (early teens) to have a facebook page and such, where she humanized/popularized the disease for the general population. A documentary company picked up the story, and now there are fluther questions about it!

@ShiningToast – Exactly! That’s what the blood work would do. Great thinking!

@Nightmare – yes, the little girl was only 10 :( Aphilotus is much more knowledgeable about her internet activites than I am. I had no idea!

@phillis I just read the wikipedia article linked to in my initial answer.

Got it! Thank you :)