Introduction: Midwifery practice is involved with clinical judgments which have direct effect on mother's and embryo's health. A midwife should be able to make vital decisions based on her knowledge and skills in emergency situations. A midwife can reach correct decisions by using critical thinking.

Materials and Methods: In this cross-sectional, descriptive-comparative study we compared critical thinking of the first and last trimester baccalaureate and post graduate midwifery students of Medical Sciences Universities of Tehran. A total of 259 qualified students of 2002-2003 educational year were selected by census method. After description the goals and methods of study, we applied California critical thinking skills test (form B) in order to measure level of student's critical thinking. This test is a valid tool for measuring critical thinking and skills, including analysis, inference, deductive reasoning, inductive reasoning and evaluation. Scores were analyzed by statistical tests (ANOVA, t test and Pearson correlation coefficient).

Results: No significant difference between total critical thinking scores of first and last trimester students was found but the scores of critical thinking of the last trimester students showed a significant decrease in Tehran University (p=0.009) and a significant increase in Iran University (p=0.007). No significant difference was found in skills of critical thinking among students. In last trimester students, scores of inductive reasoning showed a significant decrease in Tehran University (p=0.001) and a significant increase in Iran University. There was a significant decrease in evaluation ability scores in Tehran and Azad (open) Universities (p=0.002); a significant increase in these scores was found at Iran University (p=0.008).

Conclusion: According to the results of this study, despite importance of critical thinking, enough attention is not being paid to it during the educational course. The current midwifery education strategies are unable to increase level of critical thinking in students. It is essential to utilize new teaching strategies and active learning methods.