The risk of preterm birth following treatment for precancerous changes in the cervix: a systematic review and meta-analysis

Background: Studies investigating the association between treatment for precancerous changes in the cervix and risk of preterm birth have used a variety of comparison groups.

Objectives: To investigate whether treatment for precancerous changes in the cervix is associated with preterm birth (<37 weeks) and to examine the impact of the type of comparison group on estimates of risk.

Search strategy: PubMed, Embase and CENTRAL were searched for studies pubished between 1950 and 2009.

Selection criteria: Eligible studies were those that reported preterm birth outcomes for excisional and ablative treatments separately and included a comparison group.

Data collection and analysis: Pooled relative risks (RR) and 95% confidence intervals were computed using a random effects model.

Main results: Thirty eligible studies were located. Excisional treatment was associated with an increased odds of preterm birth, when compared with an external (RR 2.19, 95% CI 1.93-2.49) or internal (RR 1.96, 95% CI 1.46-2.64) comparison group. In comparison with women who were assessed but not treated, the risk estimate was smaller (RR 1.25, 95% CI 0.98-1.58). Ablative treatment was associated with an increased risk of preterm birth when an external comparison group (RR 1.47, 95% CI 1.24-1.74) but not an internal comparison group (RR 1.24, 95% CI 0.73-2.10) or untreated comparison group (RR 1.03, 95% CI 0.90-1.18) was used.

Authors' conclusions: Excisional treatment was associated with a significantly increased risk of preterm birth. It provides new evidence that some types of ablative treatment may also be associated with a small increased risk. The type of comparison group used is an important consideration when comparing the outcomes of studies.