Using the Freedom of Information Act, the RCM questioned 56 higher education institutions about staffing numbers over the past three years, and 34 responded.
The data show that the mean average student-to-midwife teacher ratio has increased over the past three years from 13:1 in 2009-10 to almost 14:1 in 2011-12.
In 2003, the RCM recommended a maximum of 10 students to every teacher. However, of the 34 institutions that responded, the number meeting this standard has dropped from four in 2009-10 to just one in 2011-12, the organisation said.
The RCM said a lower student-to-teacher ratio "allows students to be supported during clinical practice as well as in the classroom, and ensures critical linkages between midwifery theory and recent clinical practice. This also results in improved and high-quality care for mothers, babies and their families."
Cathy Warwick, RCM chief executive, said the figures reflected "an increasing tightening of the belt and squeeze on the resources, as institutions are unable to hire as many midwife teachers as they need to keep the quality of education high".
Getting midwifery teacher numbers right was important, she said, "especially given the government's welcome commitment ... to maintain the number of midwifery student places".
The RCM's figures also showed that midwifery teachers at higher education institutions are getting younger, with more teachers aged between 31 and 40.
In 2010-11, only 5 per cent of teachers were aged between 31 and 40, but this rose to 9 per cent for 2011-12. However, more than half of all teachers, or 53 per cent, were still aged 50 or above in 2011-12.