@LassOfFyvie my original comment was in response to the statement from the op:
I can only think that people want to know so that they can choose stereotypical clothes and toys and colour schemes for the bedroom.
I joined the thread to give an alternative view on why someone may chose to find out their child's sex during a scan. As said already I simply chose to take advantage of modern medicine in order to gather data about my impending child. I am fully aware that in the past people didn't find out from scans but that doesn't stop me from be allowed to discuss my more recent pregnancy any more than it should prevent you from discussing your experience from 1990.
I'm not sure why you find another woman's experience so "puzzling" and "absurd" just because it doesn't tally up with yours?
I have no idea (and have said as much already) what it is like for other people who don't find out until birth but I do know what it's like to carry a child and not know their sex because I obviously did that for half my pregnancy. We talked to it, we made plans for it, and we bought things for it. From the moment the test showed positive we loved it and were excited about our family's future.
There is a whole new unique person there- why it should make the slightest difference to bonding knowing in advance whether it is xy or xx is the bizarre bit.
The answer is right there in your question...knowing in advance. We wanted to know in advance, we found out, we were able to think and discuss important issue that may be important to raising a child of the sex we were told. For me it did matter whether it was a XX or XY, not because there was any preference not disappointment with our result but because having a female child IS different to having a male one (in my opinion).
If there was absolutely no difference in having a boy or a girl then is it so important? Why does it get announced at birth? Why is it one of the first thing you tell your friends and family? Why is there a special section of Mumsnet specifically for the discussion of women's rights and gender issues? Because the biological sex you are is a vitally important part of you as a person. Unless you chose to present yourself otherwise the sex you are dictates how society treats you, the language that is used around you, how you are educated, how you are treated by medical professions, how you are treated as an employee. It dictates what hormones are in your body, your susceptibility to certain illnesses, whether or not you can get pregnant, and if you create a child with another person your sex automatically determines whether or not you have automatic parental responsibility for that child. All of these thing play a part in parenting a child, from infancy to adulthood.
When my partner and I found out we were having a girl we both took some time to think about what that meant for our futures, child included. I am very glad I had the chance to go through that process before the birth because my birth child's birth was fucking terrible. I've seen/read on mn the joy women express about finding out the sex at birth, how finding out kept them strong and motivated, and the wonderful moments after birth etc. I don't think that's something I could have experienced, my life and my daughter's life was in danger. I had a emcs and the epidural only worked on one side of my body...I felt everything. Once my baby was out all I could think about was that now I could have more drugs to stop being in so much pain. I was so dazed I didn't know what to do when they brought her to show me so for some reason I sniffed her, then realised that I should give her a kiss. I didn't get to see or hold her for 45 min while I was being stitched up and then I was semi conscious for the next 12h. This experience traumatized me and I can imagine that not being able to fully enjoy the moment of finding out the sex on top of everything else that happened would have been another contributer to my pnd.
All of this, of course is just my experience (and my partner's). So far I have had one pregnancy and one child and this is how it happened and what choices we made. I don't believe I'm making any statements that suggest how other women think or feel or how they should conduct themselves.
It's interesting that on a thread about the importance of difference between sex and gender that fault has been found with someone wanting to learn the sex of their child. Strange that it's important enough to demand the use of the correct terminology but it's "absurd" for a woman to discuss the reasons why she found out the sex of her child during pregnancy! Amongst so much discussion about the erasure of women's identities and rights and the importance of language there's still the opportunity to find some stick to beat another women with.