Objective To determine risk factors affecting the incidence of intrauterine device (IUD) insertion-related complications and failures and, in particular, whether postcoital IUD insertions have a higher incidence of complications than routine IUD insertions.

Design Retrospective case notes analysis.

Participants The study examined 545 case notes of patients having IUD insertions at East Cheshire NHS Trust family planning clinics between 1 October 1997 and 31 December 2000.

Main outcome measures The incidence of complications at insertion, or up to 12 weeks after insertion, was determined and included failed insertion, cervical problems, syncope, bradycardia, convulsions, early perforation and early expulsion. Fourteen potential risk factors were examined to determine the effect on incidence of complications.

Results. Failed insertions were statistically more likely in women who had never previously had a vaginal delivery and also when a less experienced doctor performed the insertion. Nulliparous women were at statistically increased risk of cervical problems and bradycardia. Cervical problems at insertion also increased significantly with age. Patients who were amenorrhoeic at insertion were more likely to suffer an early IUD expulsion.

Conclusions Of the potential risk factors, nulliparity was the most important. IUD insertion failures and complications were no more common in postcoital than routine IUD insertions. In general, complications were unpredictable, indicating the need for constant vigilance and the inserting doctor being trained and prepared to deal with any complication arising.