• Dimensions of the uterine cavity;
  • displacement;
  • expulsion;
  • MLCu375;
  • nested case–control study;
  • TCu380A


To evaluate the effect of the dimensions of the uterine cavity in relation to the expulsion, or removal for displacement, of intrauterine devices (IUDs) MLCu375 and TCu380A.


A case–control study nested in a multicentre clinical trial.


Eighteen family planning clinics in China.


Forty-eight pairs of TCu380A users and 118 pairs of MLCu375 users.


The women were classified as cases if IUD expulsion or displacement occurred during the first year of follow-up after insertion. One control was randomly selected for each case matched by IUD model, centre, age, service provider for insertion, and date of insertion. Axial length of the uterine cavity (LUC) and the largest transverse diameter of the coronal section of the uterine cavity (LTD) were measured using abdominal ultrasound. We used multivariate conditional logistic regressions to estimate the adjusted odds ratios (aORs) of expulsions or displacements among women with different sizes of uterine cavity according to the quartile of LUC and LTD, respectively.


Among MLCu375 users, women with LTD ≥ 27 mm had a higher risk of expulsion or displacement (aOR 2.40; 95% confidence interval, 95% CI, 1.02–5.63), after adjusting for the volume of menstrual flow, dysmenorrhoea, parity, uterine position, MLCu375 type, and LUC. Among TCu380A users, the association between LTD ≥ 37 mm and expulsion or displacement (aOR 4.98; 95% CI 1.01–22.49) was statistically significant, after adjusting for LUC and potential confounding factors.


Our study suggests that LTD should be considered when making the decision of which IUD model to use.