Interesting thread. I think whoever said that birth order was significant is right. My situation is quite fortunate in that I am the eldest, bro in the middle and sis the youngest, so we all have our place, I'm 'special' as I am the first born (also the the most 'successful academically etc.), my bro was always the 'man of the house' (the 'fathers' in our lives were all twats and not around for long) and my sister is the baby and the most like my mum so she indulges her. She was also always the worst behaved.
However I always felt hard done by for being the eldest, I babysat day and night while my mum worked from the age of 13 and it caused a horrible relationship with my bro and sis that we are only just reparing. Also my dad has 2 little boys a lot younger than me who he has actually bought up (rather than me who he didn't see between the ages of 2 and 11 for reasons that were partly his fault and partly not). A few years ago I said to him that I felt he loved them more than me and he said of course he did, it was different
Basically I think there is often more going on than just gender. I do worry that DD and I might clash in personality as she gets older, or what if I have another child who I like more than her . I never thought that before I had a child. When I heard people worrying about not loving a subsequent child I thought it was ridiculous. But now I have had a child I worry about it more.
I think it is important to be honest with each other as mothers. We are only human and it is natural to prefer different children and find some easier. We shouldn't feel guilty about it and for those who say it is imcomprehensible, well, I imagine that makes those who do struggle with it feel even worse. You have to accept differences in children. The myth is that because we are parents we should be perfect and not even dream about treating our children differently. I have had to accept that for reasons beyond his control my dad loves his sons more than me. He is only human and can't help how he feels. It's important that we treat our children with equal respect and love though.
Sorry, that was a bit of a ramble