Objective To investigate the effect of laser conisation of the cervix on the outcome of subsequent pregnancy.
Design Case-control study.
Setting Department of Obstetrics & Gynaecology, University Hospital, Trondheim, Norway.
Subjects Three hundred and fifty-one women were treated for cervical intra-epithelial neoplasia (CIN) by laser conisation of the cervix between 1 January 1983 and 31 December 1985. The 56 women among them who had been delivered of live infants beyond 22 weeks gestation after the conisation and before 1 January 1991 were studied for the outcome of their pregnancies. For each case, two controls of equal parity and age (±3 years) were selected.
Main outcome measures The length of gestation and birthweight of the infants.
Results The median (range) length of gestation was 39 weeks (26–43) in cases compared with 40 weeks (34–42) in controls (z=−4.0, P<0.001). The median (range) birthweight was 3330 g (1150–4940) in cases and 3630 g (1610–5080) in controls (z=−3.5, P<0.001). Overall 38% of cases were delivered preterm (≤37 weeks gestation), compared with 6% of controls (P<0.0001; odds ratio 9.0, 95% CI 3.7–21.7). A logistic regression analysis of a set of possible confounding factors revealed no significant risk factors in addition to conisation for the occurrence of preterm delivery. No correlation was found between the height of the cone and the occurrence of preterm delivery in subsequent pregnancy.
Conclusion Conisation with microsurgical laser technique increases the risk of preterm delivery in subsequent pregnancies. Laser conisation in young women should be restricted to those with high grade CIN or a lesion extending into the endocervical canal.