If you girls watch the other bolyen girl, Its about our history on the king and queens the wifes couldnt carry his sons but gave birth to daughters. They kept misscarrying on having still births.
only 1 wife carried a son, and he did have another son but wansnt married to the girl.

But, I def think that it is possible to only carry one sex. I'm almost to the point of thinking my 3 were boys (def had the msot feeling after I lost this baby he was a boy) that they were boys. Because my doctor couldnt find the cause of the miscarriage.