None of what I said was dependent on the gender of the baby at all... you are mistakingly considering testosterone to be linked to 'maleness', which it is to a certain extent but not in the context we are talking about here.

The placental size theory may be the mechanism. Last thing I read on it, they had only just linked serum levels (in the mother) with brain development of the foetus and I am not sure if they had linked it directly through some mechanism. All they knew at the time was that if the mother has high serum testosterone there is a greater probability of the child being born left handed rather than right handed and the theory was that this was because testosterone influenced the growth of the brain. Its been more than ten year since I read up on this for a Psychology module project so presumably there have been advancements since