Can ultrasound predict IUD expulsion after medical abortion?

Our randomized trial compared early and delayed intrauterine device (IUD) insertion following medical abortion. In this planned substudy, we explore if endometrial thickness and initial IUD position were associated with IUD expulsion. We also describe IUD movement within the uterus during the 6 months after insertion.

We recruited women undergoing medical abortion and choosing the copper IUD for contraception (n=156). Participants were randomly assigned to early insertion 1 week after mifepristone or delayed insertion 4-6 weeks later. We measured endometrial thickness by transvaginal sonogram 1 week after abortion and IUD distance from the fundal aspect of the endometrial cavity three times: at insertion, 6-8 weeks later and at 6 months.

We analyzed endometrial thickness in 113 women, baseline IUD position in 114 women and IUD movement in 65 women. Women who expelled IUDs (n=15) had slightly thicker endometria (p=.007) and slightly lower baseline IUD positions (p=.03) than those who retained IUDs, but no clear cutoffs emerged in the receiver operating characteristic curve analysis. Retained IUDs commonly moved up and down throughout the 6 months (from 14 mm towards the fundus to 32 mm towards the cervix). Overall, retained IUDs moved a median of 2mm towards the cervix between insertion and exit (p<.0001).

After medical abortion, the risk of IUD expulsion increases with thicker endometria and lower baseline position. Since no clear cutoffs emerged in the analysis and expulsion remained uncommon even with thicker endometria, we do not recommend restricting IUD insertion based on ultrasound data.

Copper T IUDs often move within the uterus without expelling. Expulsion is uncommon, and we do not recommend restricting IUD insertion based on ultrasound data.