Uterine perforation is a rare, but serious complication of IUCD insertion, and is often silent. The incidence rate is reported between 1.6 and 2.2 in 1000. Aberrant IUCDs can be identified using most imaging modalities, with US being the recommended first line investigation, in all women in whom the ‘strings’ cannot be visualized, followed by orthogonal plain film views as second line. CT can be used in complex cases where visceral involvement or surgical difficulty is suspected.

In the puerperium the incidence of uterine perforation by IUCD is higher, and insertion of an IUCD is not recommended in women with a hyperinvoluted small uterus. The uterus during lactation is softer and can be atrophic, and hyperinvolution of the uterus is associated with lengthy amenorrhea postpartum during lactation. 

Lack of visualization of strings at follow-up examination of any woman with an IUCD should raise the possibility of silent uterine perforation, especially in breastfeeding women, and should prompt further investigation. A pelvic US should always be performed in the first instance for all cases of ‘missing strings’.