Research published by scientists at the University of Adelaide in the journal Molecular Human Reproduction in 2014 showed that newborn girls may be healthier on average because a mother’s placenta behaves differently depending on the sex of the baby. With female fetuses, the placenta does more to maintain the pregnancy and increase immunity against infections. Why this is, nobody understands. It could be because, before birth, the normal human sex ratio is slightly more skewed toward boys. The difference after birth might simply be nature’s way of correcting the sex balance.
