Objective: To study whether loop electrosurgical excision procedure (LEEP) conization is associated with preterm birth and to study the effect of cone size on preterm birth.
Methods: This was a retrospective cohort study from Southern Finland conducted from 1997 to 2003, with a follow-up for subsequent births until 2006. We identified the cases from the Hospital Discharge Register and Medical Birth Register and collected additional information from the hospital records. Our cohort consisted of 624 women who delivered after LEEP conization. We calculated expected preterm birth rates by using the Medical Birth Register data. In subgroup analysis (n=258 women) we used internal controls, ie, deliveries before the treatment. The main outcome measure was preterm birth rate in different subgroups.
Results: The risk for preterm delivery (before 37 weeks) was increased almost threefold (relative risk [RR] 2.61, 95% confidence interval [CI] 2.02-3.20; number needed to treat for harm=14) and repeat treatments more than fivefold (RR 5.15, 95% CI 2.45-7.84; number needed to treat for harm=5) after LEEP conization compared with the background rate of preterm birth (4.61%). Large or repeat cones increased the risk twofold (RR 2.45, 95% CI 1.38-3.53) when compared with small or medium-sized cones. For women having a birth before and after LEEP conization, the preterm birth rate was 6.5% before and 12.0% after the procedure (RR 1.94, 95% CI 1.10-3.40; number needed to treat for harm=18). Adjusting for maternal age, parity, or both did not change the results. The risk for preterm birth was especially increased (RR 3.38, 95% CI 2.31-4.94) among women without previous preterm birth.
Conclusion: Loop electrosurgical excision procedure surgery of the cervix predisposes patients to preterm birth. Loop electrosurgical excision procedure conization increased the risk for preterm birth especially among women without previous preterm birth. The rates were highest after repeat procedures.
Level of evidence: II.