As soon as conception occurs I thought? They were able to tell me at lucas' 5 month scan.

I'm not too sure but I really want to know ow even though I know I can't but I have a feeling i'm having a little girl, i'm going to see if they can tell me the sex when I go for my scan next month

Oh ok, I wasnt sure if u meant when is the babys sex decided in the uterus, or when u can be told on the scan. At my 12 week scan with my son they didnt tell me. I was told at the 5 month one.

I did mean in the uterus because I was just curious, i'll be 13 weeks when they do my scan so hopefully they will be able to tell me, they managed to tell my sister with her first she chose not to find out with bubs number 2

It is usually visible around 18-22 weeks on an u/s (if baby is co-operative).

But the actual scientific bit - is that the sex is decided by the sperm that fertilises it.

All eggs have x chromosomes, sperm have x or y chromosomes.
If you get a x sperm you get a girl, if you get a y sperm you get a boy.
Two y chromosomes are not possible.
This is why we do not need men technically. It is exceptionally unethical but is possible albeit illegal and you wouldn't find any doctor who would do it.
But you can make a human embyro by stripping the nucleus of an egg (as they do to sperm for ivf) and implanting it into the nucleus of another egg. You would get a girl everytime.
This can not be done for two men by using 2 sperm as sperm do not have the neccessary information on how to make the cells divide and grow.

I remember reading somewhere that the outside genitalia starts to form around 13 weeks so usually its not visible till around 16 weeks.

I knew that sperm has either a x or y and that makes the sex but I just wanted to know when you can tell

Yep, it's decided from the moment that sperm fertilizes the egg. &.I've *heard* of girls finding out when they were like 13wks... But .I'm not sure if that's true. I'll (hopefully) be finding out tomorrow at my 22wk scan!

If you feel your having a girl then you probably are.

I .K.N.E.W. I was having a boy, the feeling was there from the start and never went away, and it turns out I was having a boy!

My first instinct with this one was girl. My mom says girl, my best friend's mom says girl.. But everyone else is saying boy. Guess we'll find out tomorrow... :d

I was absolutely positive I was having a girl, I felt it. I found out at 18 weeks that he was a boy.

Personally, I wouldn't trust anything before 18 weeks. Yes, people claim to have been told at 13 weeks but then again they have a 50/50 chance of being right.

One of my good friends had twins &she said at her 12wk ultrasound, the doctor told her they were both girls... 12wks!! They *did* end up both being girls, but honestly, is that even possible? Is was just a regular ultrasound, not a high tech one or anything.