Objectives To study whether the increasing severity of cervical intraepithelial neoplasia (CIN) by LEEP (loop electrosurgical excicion procedure) cone correlates with the risk for preterm birth. We also wanted to study whether the time period from LEEP or repeat LEEP correlates with the risk.

Methods Retrospective register-based study from Finland during 1997–2009. We collected data from the Hospital Discharge Register. We linked the data with data from the Finnish Medical Birth Register. The study population consisted of 20 011 women who had LEEP during 1998–2009 and a subsequent delivery during 1997–2009. Controls were women with no previous LEEP (n=430 975). The main outcome measure was preterm birth (<37 gestational weeks) rate.

Results The risk for preterm birth was increased after LEEP (OR 1.82, CI 1.62 to 2.03). In primiparous women this risk was slightly lower OR 1.61 (CI 1.42 to 1.83). Repeat LEEP was associated with almost threefold risk for preterm birth (OR 2.71, CI 1.98 to 3.69). Increasing severity of CIN did not correlate with the preterm birth rate. LEEP for carcinoma in situ or microinvasive cancer, however, increased the risk threefold (OR 3.25, CI 1.92 to 5.50). The risk was also increased for HPV-related non-CIN lesions (OR 2.55, CI 1.72 to 3.78). Time period since LEEP was not associated with the risk for preterm birth. Adjusting for maternal age, parity, socio-economic status, or marital status, or history of previous preterm birth did not change the results.

Conclusion The risk for preterm birth was increased after LEEP, but was not associated with the severity of CIN. Repeat LEEP had highest risk. Unnecessary LEEP should be avoided especially among young women.