Role of uterine forces in intrauterine device embedment, perforation, and expulsion

Abstract

BackgroundThe purpose of this study was to examine factors that could help reduce primary perforation during insertion of a framed intrauterine device (IUD) and to determine factors that contribute in generating enough uterine muscle force to cause embedment and secondary perforation of an IUD. The objective was also to evaluate the main underlying mechanism of IUD expulsion.MethodsWe compared known IUD insertion forces for “framed” devices with known perforation forces in vitro (hysterectomy specimens) and known IUD removal forces and calculated a range of possible intrauterine forces using pressure and surface area. These were compared with known perforation forces.ResultsIUD insertion forces range from 1.5 N to 6.5 N. Removal forces range from 1 N to 5.8 N and fracture forces from 8.7 N to 30 N depending upon device. Measured perforation forces are from 20 N to 54 N, and calculations show the uterus is capable of generating up to 50 N of myometrial force depending on internal pressure and surface area.ConclusionPrimary perforation with conventional framed IUDs may occur if the insertion pressure exceeds the perforation resistance of the uterine fundus. This is more likely to occur if the front end of the inserter/IUD is narrow, the passage through the cervix is difficult, and the procedure is complex. IUD embedment and secondary perforation and IUD expulsion may be due to imbalance between the size of the IUD and that of the uterine cavity, causing production of asymmetrical uterine forces. The uterine muscle seems capable of generating enough force to cause an IUD to perforate the myometrium provided it is applied asymmetrically. A physical theory for IUD expulsion and secondary IUD perforation is given.

Prevention of intrauterine contraceptive device expulsion and intolerance: Determination of the anchor mechanism

“…In this case the likelihood of problems (e.g, expulsion, embedment) in any group, nulliparous or multiparous is drastically reduced [26]. If the transverse arm of the IUD is too long as in Figure 4A-C, then the IUD will either be expelled due to symmetrical expulsive forces or the anchor becomes pathological, causing embedment and bleeding due to asymmetrical uterine forces acting on the IUD [27]. In the latter case, the uterus may not be capable of expelling the IUD.…”

Malposition and displacement of intrauterine devices–diagnosis, management and prevention

“…If the IUD is not fully expelled, embedment and/or secondary perforation of the IUD may occur. The imbalance between the size of the IUD and that of the uterine cavity can result in the production of asymmetrical uterine forces, which can increase patient discomfort especially while menstruating [16]. Hubacher's review of copper IUDs revealed that nulliparous women experience higher rates of total expulsion and removals for bleeding and/or pain compared with parous women [17].…”

“…Incompatibility between the IUD and the endometrial cavity will provoke uterine contraction in an attempt to expel the IUD. The impact of uterine forces can be significant if the transverse arm of the IUD/IUD is significantly greater than the fundal transverse diameter [16]. These forces can compress, distort, displace, and expel the IUD, particularly if the IUD is not capable of adaptive changes [30].…”

How to become Proficient with Insertion of Frameless IUDS?

“…The attachment to the fundus of the uterus minimizes the risk of expulsion [22,23]. Long term comfort, especially for those women (e.g., nulliparous and adolescent women) with a small or distorted uterine cavity, and for women who have experienced problems with framed IUDs can be achieved with a frameless IUD ( Figure 9) [19,24].…”