We had a car seat - one that does from newborn to 4 years and isn't carryable. We'd also had the fit checked by a professional. The midwife didn't believe me that it wasn't the "normal" travel system kind and tried to insist we took it out of the car and brought it into the hospital. After a lot of arguing, she wrote in my notes that I was being difficult and made me sign that I was taking the risk with my baby before she would discharge me.
I complained and asked that if midwives were going to be like this, they got some training in what travel options were available - not just group 0 turn-your-arms-to-gorilla's-ones car seats.