What happens to CNMs if there are too many obstetricians in 1990?
D006286:Health Planning Councils; D006801:Humans; D009721:Nurse Midwives / Q000706:statistics & numerical data*; D009774:Obstetrics / Q000639:trends; D010820:Physicians / Q000600:supply & distribution; D014481:United States; D000078329:Workforce