Objective: Studies in animals and human muscle have demonstrated differential splicing of the insulin-like growth factor-1 gene in response to mechanical strain and damage. We conducted a study on the expression of insulin-like growth factor-1 splice variants in the levator ani muscle after the first vaginal delivery. Study design: Ten women were recruited after the first vaginal delivery. Biopsy specimens were taken vaginally of the pubovisceral component of the levator ani muscle. Five nonpregnant women were recruited as control subjects. Samples were processed with real-time quantitative polymerase chain reaction, with specific primers for the insulin-like growth factor-1 splice variants. Results: Insulin-like growth factor splice variants mechano growth factor and insulin-like growth factor1Ea were significantly up-regulated (100-and 1000-fold) in the delivery population, compared with control subjects (P = .012 and .04, respectively). Statistical analysis indicated a correlation between the expression of the insulin-like growth factor-1 splice variants and the length of the second stage. Conclusion: These results show that damaged levator ani muscle results from stretch and overload after the first vaginal delivery.
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