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.