A state report released yesterday found a wide variation in the frequency of caesarean sections at Massachusetts hospitals, in an analysis restricted to first-time mothers with low-risk pregnancies who would be least likely to need the surgery. The Department of Public Health report showed that the caesarean rates for these low-risk women ranged from 10% to 35% among the hospitals in 2009, the most recent year for which the data are available. "This degree of variation suggests all are not practicing the procedure at the ideal rate," Lauren Smith, MD, the agency's medical director, said in an interview. State health officials, saying they were surprised and mystified by the wide variation, released the findings at a meeting yesterday with representatives from 49 hospitals that perform deliveries in the state. The officials hope to get the hospitals' help in rooting out unnecessary caesareans.