Duration of Pregnancy After Carbon Dioxide Laser Conization of the Cervix: Influence of Cone Height LUIGI RAIO, MD, FABIO GHEZZI, MD, EDOARDO DI NARO, MD, RICARDO GOMEZ, MD, AND KLAUS P. LU ¨ SCHER, MD Objective: To determine if carbon dioxide laser conization of the cervix is a risk factor for preterm delivery in subsequent gestations and to evaluate whether there is any relationship between cone height and duration of pregnancy. Methods: Patients of fertile age who had carbon dioxide laser conization were followed for reproductive events. Cases were matched one-to-one with controls for known risk factors for preterm delivery. Pregnancy duration, rate of preterm birth, and mode of delivery were studied. Paramet- ric and nonparametric tests were used for statistical analysis. Logistic regression analysis and Cox proportional hazard modeling were used to investigate the relationship between cone height and subsequent preterm delivery. Results: Sixty-four women with singleton pregnancies after carbon dioxide laser conization and 64 controls were included in the study. Overall, no difference was found in the rate of preterm delivery and duration of pregnancy. However, women with cone height of at least 10 mm had a higher rate of preterm delivery than either those with cone height less than 10 mm (five of 23 versus one of 41, P  .01) or the controls (five of 23 versus three of 64, P < .05). Cone height of at least 10 mm remained significant in predicting the occurrence of preterm delivery and the duration of pregnancy after adjusting for known risk factors (odds ratio 11.1, P < .05). Conclusion: Cone height of at least 10 mm is an indepen- dent risk factor for the duration of pregnancy and for the occurrence of preterm delivery in the subsequent gestation. (Obstet Gynecol 1997;90:978 – 82. © 1997 by The American College of Obstetricians and Gynecologists.) Several authors 1–5 have reported a higher incidence of preterm labor and delivery in patients with a history of cervical conization. However, most of these operations were conducted using cold knife techniques. Laser conization was introduced in 1973 by Kaplan et al 6 and is currently used widely. Yet, the pregnancy outcome of patients undergoing this procedure is still controversial. A recent retrospective study 7 reported that laser coniza- tion was responsible for a sixfold increase in the rate of preterm delivery in subsequent pregnancies. On the other hand, Spitzer et al 8 did not find a significantly increased rate of preterm delivery in patients undergo- ing either laser vaporization or laser excision. The purpose of this study was to determine if carbon dioxide laser conization of the cervix is a risk factor for preterm delivery in subsequent gestations and to eval- uate whether there is any relationship between cone measurements and duration of pregnancy. Materials and Methods This study was conducted at the Department of Obstet- rics and Gynecology of Mu ¨ nsterlingen, Kantonsspital, Switzerland, from August 1, 1986, to December 31, 1994. Laser conization using the technique proposed by Dorsey and Diggs 9 was performed in 228 women younger than 35 years of age with cervical intraepithe- lial neoplasia (CIN). Patients were observed for repro- ductive events. Twenty-six patients were lost to follow- up. By December 31, 1996, 117 pregnancies occurred in 78 patients who had undergone laser conization. If women conceived more than once, only the first subse- quent gestation was included in the analysis. Sixty-four of these 78 patients with singleton gestations (cases) were included in the study. Laser conization in all these cases was performed by the same operator. Fourteen patients were excluded because of the following rea- sons: voluntary termination of pregnancy (n = 4), twin gestation (n = 3), first-trimester miscarriage (n = 2), fetal death (n = 1), ectopic pregnancy (n = 1), second- From the Department of Obstetrics and Gynecology, Kantonsspital, Mu ¨ nsterlingen, Switzerland; the Department of Obstetrics and Gyne- cology, II Faculty of Medicine, University of Pavia, Varese, Italy; the Department of Obstetrics and Gynecology, University of Bari, Bari, Italy; and the Maternity of Sotero del Rio Hospital, Puente Alto, Chile. 978 0029-7844/97/$17.00 Obstetrics & Gynecology PII S0029-7844(97)00489-4