When I had dd I asked for 38 weeks because I was in a lot of pain but he told me that about 40% or so of babies born at 38 weeks require some level of oxygen and their hospital policy for electives is 39 weeks so that is when dd was born. Even at 39 weeks dd's oxygen levels were too low to begin with and they almost had to take her to the scn but they stabilized at the last second.