I get asked this all the time. Although it varies from one person to another, the short answer is, a Doula mother's the mother, and is involved with supporting and empowering the whole family. She will also cook, run errands, do family laundry, help out with siblings, as well as taking care of the baby too. Some are Newborn Care Specialists as well, so the family gets the best of both worlds.
A Newborn Care Specialist focuses on the care and development of the baby only. She will help establish a schedule, and sleep train the baby if desired. She is called a specialist for a reason. She should be able to answer any questions you might have about your baby. She may or not be trained, so always ask. A Baby Nurse is a Newborn Care Specialist who is also a RN, LPN, or has some kind of nursing degree. However, neither a Baby Nurse/Newborn Care Specialist nor a Doula, is a substitute for medical advice. The Baby Nurse/ NCS will also keep the nursery stocked and organized, log all activities, and take care of the baby's laundry, bottle washing, and sterilizing etc. We feed the baby through the night, and get them resettled. We can set the baby on a path to sleeping through the night, by instilling some healthy sleep habits, and ensuring the baby is sleeping in an environment that promotes sleep. A good Baby Nurse/NCS will also make sure a nursing mom has drinks and snacks, as she takes the baby to mom. Baby Nurses/NCSs often move in with the family, and work 24/7 around the clock with breaks.
I advise families to make a list of what duties are important to them to have help with, and decide whether a Baby Nurse, Newborn Care Specialist, or a Doula is the best fit for their family. Interview several candidates. Personality fit is just as important in the decision making process.