Low-lying or Malpositioned Intrauterine Devices and Systems
Low-lying or Malpositioned Intrauterine Devices and Systems
Early studies showed that in women who had become pregnant with an IUD in situ, the IUD was more likely to be found low-lying within the cavity than at the fundus. The conclusion was that low-lying devices are more likely to fail. In support of this is the finding that failure is more likely when a previous IUD has been expelled, suggesting that downward displacement of the IUD could be a cause of failure. However, if this is the case, with reported rates of incidental findings of malposition of between 7% and 16%, it seems surprising that failure rates are not higher. The studies varied in the level of detail given on what constituted a malpositioned device, which makes comparison of the various study findings difficult.
It may be that an IUD that has failed is pushed out of a normal position by the enlarging gestational sac. It has been shown that IUDs move within the uterus during the menstrual cycle and may move from a normal to an abnormal position or vice versa over time. Thus, it is likely that IUDs do move within the uterus during early pregnancy if failure has occurred. Indeed, one published case study reports on an IUD that was noted to be low-lying in the uterus and cervix in early pregnancy but which migrated vertically during pregnancy, perforating the fundus and ultimately migrating into the peritoneal cavity.
The IUS has a different mechanism of action to the copper IUD, and the Pakarinen and Luukkainen trial does suggest that a similar device may be equally effective even when displaced to the cervix. Ultimately, whilst it may be that the IUD and IUS still provide contraceptive effect when displaced from their optimal position at the fundus, there is no definitive evidence that this is the case. To be sure of providing the best contraceptive effect, it may remain best practice to replace an incidentally-found low-lying device, although an attempt may be made to correct the position of an IUS. This is particularly relevant for younger women, who have higher fertility.
The published evidence regarding symptoms when an IUD is malpositioned is contradictory and no randomised trials have been conducted. The advent of 3D ultrasound technology may provide more accurate data to help answer this question in the future. Given that some studies have shown a link, it may be worth considering replacing a low-lying device in symptomatic women. A cautionary tale is provided by Braaten et al., who showed a higher unplanned pregnancy rate in women whose malpositioned devices were removed and who did not adopt another highly effective method of contraception. If a low-lying IUD is removed because of symptomatology or ultrasound findings, it is important to initiate another method of contraception at the same time.
The evidence demonstrates that IUDs can move within the uterine cavity, both in an upward or downward direction, particularly in the initial months after insertion.
Braaten et al. was the only study identified by our systematic review that looked at postpartum insertion and malpositioning directly and these authors reported no statistically significant increase in malpositioned IUDs after postpartum insertion. This was a small, retrospective study and so prospective data would be a valuable addition to this area of research.
Discussion
Is Contraceptive Failure More Likely With a Malpositioned IUD/IUS?
Early studies showed that in women who had become pregnant with an IUD in situ, the IUD was more likely to be found low-lying within the cavity than at the fundus. The conclusion was that low-lying devices are more likely to fail. In support of this is the finding that failure is more likely when a previous IUD has been expelled, suggesting that downward displacement of the IUD could be a cause of failure. However, if this is the case, with reported rates of incidental findings of malposition of between 7% and 16%, it seems surprising that failure rates are not higher. The studies varied in the level of detail given on what constituted a malpositioned device, which makes comparison of the various study findings difficult.
It may be that an IUD that has failed is pushed out of a normal position by the enlarging gestational sac. It has been shown that IUDs move within the uterus during the menstrual cycle and may move from a normal to an abnormal position or vice versa over time. Thus, it is likely that IUDs do move within the uterus during early pregnancy if failure has occurred. Indeed, one published case study reports on an IUD that was noted to be low-lying in the uterus and cervix in early pregnancy but which migrated vertically during pregnancy, perforating the fundus and ultimately migrating into the peritoneal cavity.
The IUS has a different mechanism of action to the copper IUD, and the Pakarinen and Luukkainen trial does suggest that a similar device may be equally effective even when displaced to the cervix. Ultimately, whilst it may be that the IUD and IUS still provide contraceptive effect when displaced from their optimal position at the fundus, there is no definitive evidence that this is the case. To be sure of providing the best contraceptive effect, it may remain best practice to replace an incidentally-found low-lying device, although an attempt may be made to correct the position of an IUS. This is particularly relevant for younger women, who have higher fertility.
Are Women With a Malpositioned IUD/IUS More Likely to Experience Symptoms of Pain and/or Bleeding?
The published evidence regarding symptoms when an IUD is malpositioned is contradictory and no randomised trials have been conducted. The advent of 3D ultrasound technology may provide more accurate data to help answer this question in the future. Given that some studies have shown a link, it may be worth considering replacing a low-lying device in symptomatic women. A cautionary tale is provided by Braaten et al., who showed a higher unplanned pregnancy rate in women whose malpositioned devices were removed and who did not adopt another highly effective method of contraception. If a low-lying IUD is removed because of symptomatology or ultrasound findings, it is important to initiate another method of contraception at the same time.
Can an IUD/IUS Move Within the Uterine Cavity?
The evidence demonstrates that IUDs can move within the uterine cavity, both in an upward or downward direction, particularly in the initial months after insertion.
Is Postpartum Insertion Associated With Increased Malpositioning of an IUD/IUS?
Braaten et al. was the only study identified by our systematic review that looked at postpartum insertion and malpositioning directly and these authors reported no statistically significant increase in malpositioned IUDs after postpartum insertion. This was a small, retrospective study and so prospective data would be a valuable addition to this area of research.
