Another reason to be glad you're a girl. Preemie boys do worse than preemie girls with things like low blood pressure, brain hemorrhaging, pregnancy toxemia, infection, separation of the placenta, preeclampsia, and premature loss of amniotic fluid, and one researcher says she knows why. She thinks it is because boy fetuses mature later than girl fetuses.
This is plausible. I guess the way to check it would be to see if boys born at, say, 32 weeks do as well as girls at, say, 27 weeks.