Objective    To investigate the changes of the expressions of collagens type Ⅰ

type Ⅲ，and MMP-1 in the levator ani muscle of pregnant women.     Methods    Twenty women after vaginal delivery [age mean （28±4） years

duration of pregnancy mean （39±3） weeks] were the late pregnant group and 5 women with perineal laceration but without delivery [age mean （25±4） years] served as the control group. All of them accepted our informed consent. Their levator ani muscle tissue samples were extracted. Semi-quantitative reverse transcription polymerase chain reaction (RT-PCR)

haematoxylin-eosin (HE) staining and immunohistochemistry were performed to detect the expressions of collagens type Ⅰ

type Ⅲ，and MMP-1.     Results    The muscle fiber of levator ani from the late pregnant group was more hypertrophy than that of the control group

in an close but bit of disordered arrange without necrotic appearance. The late pregnant group showed increased positive staining of collagen types Ⅰand Ⅲ and elevated ratio of type Ⅰ/Ⅲ (P0.05). The optical density(OD) values of MMP-1 mRNA in the late pregnant group was lower than control group (P0.05).     Conclusion    Muscle fiber of levator ani from the late pregnant group is more hypertrophy than that of the control group

and accommodation of collagen is increased relatively.