It is common knowledge amongst OBGYNs that a short cervix is associated with a risk of preterm delivery, and that if you have a history of a LEEP or other excisional procedure for cervical dysplasia, you also have an increased risk of preterm birth. Interestingly, a meta-analysis in 2014 revealed that women with a history of LEEP have a similarly increased risk of preterm birth to women with a history of cervical dysplasia and no LEEP. So, what’s to blame for the increased risk of preterm birth? A classic question of the chicken or the egg. Was it the cervical dysplasia itself or the excisional procedure?
The October 2015 Gray Journal features a study trying to tease apart the impact of cervical dysplasia, excisional procedures, and short cervix on the risk for preterm deliveries. Dr. Miller and colleagues from Northwestern University examined a cohort of over 18,000 women with singleton pregnancies and routine cervical length measurement at 18-23.9 weeks. 16% had a history of prior dysplasia alone and 7% had a history of an excisional procedure.
As expected, women with no history of dysplasia or excision had the lowest risk of preterm birth and short cervix. However, unlike the prior meta-analysis, in this study, a prior excisional procedure was associated with higher risk of preterm birth at 8.4%, but cervical dysplasia alone was not associated with a higher risk of preterm birth at 6.5% compared to 6.4% for women with no history of dysplasia or procedure.
Perhaps their most interesting finding was that, even after they controlled for the effects of a short cervix on preterm birth, having a history of prior excision was still a significant risk factor for preterm birth. This suggests that the reason a prior excision increases preterm birth risk goes beyond just physically shortening the cervix. The authors suggest that perhaps the procedure changes cervical collagen remodeling. Nevertheless, this large cohort study suggests that cervical dysplasia alone is not to blame and we need further research to understand why excisional procedures are linked with preterm birth, even beyond a short cervix.