If you want to be a neonatal surgeon and an obstetrician?

if you want to work at a small hospital that has about one main person in each field of surgery, you can be both an obstetrician and a neonatal surgeon. my question is, would you do your residency to become a pediatrician? and also i would think that you would have to do a fellowship for both of them but could you complete your fellowship as a neonatal surgeon and right then start one as an obstetrician?