Before I start ruminating on this particular issue, please read this article from the UK's Telegraph.
This is certainly an ethical question. I was most troubled by the quote: "There is very little evidence that allowing parents to choose the sex of their child would have any imbalancing effect on society."
Sorry, no, there is plenty of evidence. Look at China. With their one child a family rule, many female babies or fetuses are killed or aborted. The number of male to female children in China is staggering. China is going to go into serious population decline within a generation or two because there is not a balance of male to female.
If choosing your unborn child's sex is not unethical...what is unethical? What's next...Genetic engineering? Wait, is that not what this is? What time is it?...oop, 1984 already.