a lot of it will depend on your age and history - we weren't able to put two embryo's back until we'd had X number of failed cycles/early miscarriages. they look at maternal age and history - if you're under 30, with no long term history of failed assisted conception cycles (i think at my clinic it is four attempts) or multiple failed pregnancies, they are very reluctant to put two embryo's back. i was only given the option after 3 early miscarriages, 3 IUI's and one failed IVF fresh transfer. before that, it had been an attitude of "not a chance".

and you're right - a healthy baby is so much more important than the gender!