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Cone biopsy increases risk of preterm birth

Obstetrics and gynaecology

Obstetrics and gynaecology

Pregnant women who have had a cone biopsy are at increased risk of late abortion and preterm birth.

Data have been comprehensively collected in Norway for several decades on birth statistics as well as cancer and pre-malignant conditions. The study investigated pregnancy outcomes between 1967 and 2003 and included more than 15,000 women with a previous cone biopsy. These patients were compared with two control groups: women who had not had a cone biopsy (around two million patients) and women whose operation was carried out after pregnancy (around 57,000 patients).

Women with a pre-pregnancy cone biopsy were more likely to have a preterm delivery compared with women whose cone was inserted after pregnancy and those who did not undergo the procedure (17.2% compared with 6.7% and 6.2% respectively). Women who had a cone inserted before pregnancy were also at increased risk of late abortion (<24 weeks) and very early preterm birth (24-27 weeks), with relative risks of 4.0 and 4.4 respectively. Gestationally adjusted birthweight was not analysed as smoking data were not available.

Surgical techniques changed during the study period. Originally, all cones were knife cut, but laser biopsy was introduced in the 1980s and followed by LLETZ (large loop excision of the transformation zone) in the 1990s. These newer techniques usually remove smaller volumes of cervical tissue. A recent meta-analysis looking at excisional and ablative procedures concluded that knife biopsy and radical diathermy of the cervix appear to be more damaging to cervical function in pregnancy.1

The age at which cervical cytological screening commences in England has recently been raised to 25 years. When planning the investigation and treatment of cervical intraepithelial neoplasia, the woman's reproductive potential should always be considered.

It appears that larger volume and hot ablative procedures significantly increase the risks of preterm birth and perinatal mortality.

Albrechtsen S, Rasmussen S, Thoresen S et al. Pregnancy outcome in women before and after cervical conisation: population based cohort study. BMJ 2008;337:1343-8

Reviewer

Dr Chris Barclay
GP, Sheffield

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