• conisation;
  • preterm delivery

Please cite this paper as:Ørtoft G, Henriksen T, Hansen E, Petersen L. After conisation of the cervix, the perinatal mortality as a result of preterm delivery increases in subsequent pregnancy. BJOG 2010;117:258–267.

Objective  To determine the effects of one or two conisations on preterm delivery and perinatal mortality in subsequent pregnancies.

Design  A population-based cohort study.

Setting  Aarhus University Hospital.

Population  Preterm delivery and mortality rates were evaluated in 721 deliveries after one conisation, and in 37 deliveries after two conisations, and were compared with 390 deliveries after dysplasia and 74 552 deliveries that were not preceded by conisation or dysplasia.

Methods  Cox regression was used to evaluate preterm delivery rates and perinatal mortality.

Main outcome measures  Birthweight, gestational age (prior to 28, 32, and 37 weeks of gestation, respectively) and perinatal mortality.

Results  The risk of preterm delivery was increased after one conisation [adjusted hazard ratios (95% CI): <37 weeks, 2.8 (2.3–3.5); <28 weeks, 4.9 (2.5–9.7)], and was further increased after two conisations [adjusted hazard ratios (95% CI): <37 weeks, 9.9 (6–17); <28 weeks, 9.8 (1.4–70)], compared with no conisation. One conisation was associated with an increased perinatal mortality [<28 weeks, 9.9 (4.0–25)]. All three methods of conisation [large loop excision of the transformation zone, electroknife and cold knife] increased the risk of preterm delivery.

Conclusions  A single conisation was associated with a 2.8-fold increased risk of perinatal death, most likely because of a 4.9-fold increase in extreme preterm delivery. Only 37 patients had two conisations, and the results showed a ten-fold increase in the risk of preterm delivery.