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Intrauterine devices are on the move Your most pressing questions addressed
By Regina-Maria Renner, MD, MPH, Fellow in Family Planning and
By Alison Edelman, MD, MPH, Associate Professor, Assistant Director of the Family Planning Fellowship, Department of Obstetrics and Gynecology, Oregon Health & Science University, Portland
A 25-year-old G3P1021 presents to clinic concerned that her intrauterine device (IUD) strings feel longer. She is otherwise asymptomatic. Her IUD was placed five months earlier without complications, and it was noted that her stings were cut to 3 cm. On exam, the IUD strings are 4 cm long. The exam is otherwise unremarkable, and the IUD stem cannot be seen or felt. An ultrasound shows a copper IUD in the lower uterine segment, but above the cervix. What now? This case scenario might generate several questions and/or concerns. Is your inclination to remove the IUD? If so, wait and read further.
Where in the uterus does the IUD normally "live"?
Faundes et al prospectively followed a cohort of 214 women after copper T IUD (CuIUD, Paragard) insertion.1 With serial ultrasound exams, they assessed several measurements that were performed at insertion, 30 days later, and 90 days later. Most women had an IUD-to-myometrium distance that increased with time (distance at insertion: 7 mm; 30 days: 9 mm; 90 days: 10 mm). Based on this information, they defined "correct" placement with an IUD-to-myometrium cutoff measurement of 7 mm. In applying this measurement at the time of insertion and at 90 days, 17 and 21 IUDs were considered "misplaced." Leaving these IUDs in situ revealed that only six remained "misplaced" after 90 days, one expelled (but this IUD actually had been in a normal position at 30 days), and two were found to be in the intracervical canal and removed. No pregnancies were reported during the study.
This study illustrates that IUD position is not static and there is a small amount of movement within the uterine cavity, especially in the vertical direction between the fundus and lower uterine segment. More importantly, visualizing the IUD in the lower uterine segment or using a cutoff measurement to define "misplacement" did not predict expulsion. Additionally, some of these measurements can vary significantly during the menstrual cycle, 5 mm or more, secondary to endometrial thickness.
A retrospective cohort study of 214 women assessed IUD location using ultrasound over six months after insertion of a Multiload375 (ML375) IUD (a copper-based IUD) (n = 107) or a levonorgestrel-releasing (LNG) IUD (n = 107).2 The distance between the top of the IUD and the junction between endometrium and uterine cavity (IUD-ED) was measured. Investigators defined a "partial expulsion" as an IUD-ED > 10 mm, and they recommended removal based on this definition. Partial and complete expulsions were not reported separately in this study. The IUD groups did not significantly differ regarding age, parity, sounded uterine length, or history of IUD expulsion. Correct position was verified at the time of insertion.
At six weeks, partial or complete expulsion was noted in 11% in the ML group vs 4% in the LNG group (P = 0.06). At six months, partial or complete expulsion again was noted to be higher in the ML group (P < 0.05). Partial or complete expulsion was found to be associated with increasing parity and history of IUD expulsion. Again, no pregnancies were observed. This study concluded that LNG IUDs have a lower expulsion rate; however, the data are insufficient to draw such conclusions. ML375 IUDs are known to have higher expulsion rates than T-shaped devices, such as the LNG- and Cu-IUDs.3
When and how should we assess IUD location?
In a prospective cohort of 436 CuIUD users, Petta et al studied transvaginal ultrasound to assess correct IUD location.4 Groups received an ultrasound at 30-40 days post-insertion vs clinical exam alone. This study defined "correct" placement as less than 3 mm between IUD and endometrium at the fundus. Women were matched by age and parity and followed for one year to determine expulsion rates. This study did not separate true expulsions from those removals performed for an IUD position of more than 3 mm from the endometrium.
Among the ultrasound cohort (n = 235), 34 IUDs were found to be "misplaced" and were removed; 22 had a new IUD inserted, of which seven expelled later. One true expulsion was found in the ultrasound cohort. In the routine care group, 10 women experienced true expulsions. One pregnancy occurred in the latter group at 11 months. Although the ultrasound cohort had a lower number of "true" expulsions, the total number of IUDs removed due to an arbitrary cutoff value makes the number needed to treat to support the routine use of ultrasound unreasonably high, or 34 IUD removals to prevent nine expulsions. It's likely that most of these removals were unnecessary and would not have ended in expulsion since Faundes showed the IUD to endometrium measurement varies significantly during the cycle.1 In addition, not all of these 34 women chose to have another IUD, which means they are probably using a less effective method of birth control. Finally, the number of expulsions that occurred in the routine care group is higher than expected (4%), which makes one think there were insertion technique issues in this group as compared to the ultrasound group. As groups were enrolled based on days of the week, perhaps less experienced providers were placing IUDs in this group?
De Kroon et al also assessed the use of ultrasound to monitor the position of an IUD after insertion.5 This prospective cohort of 195 women with high study retention (93%) compared serial clinical IUD string length with ultrasound at the time of insertion and six weeks thereafter. A distance of more than 5 mm between IUD and endometrium on ultrasound was considered "dislocated." Although various IUD types were included in the study, more than half were LNG IUDs (58.5%). Immediately after insertion, ultrasound identified 7.7% of IUDs as "dislocated" six weeks thereafter, only 4% were identified as dislocated. Consistent with the results of the Faundes et al1 study, the majority of IUDs classified as "dislocated" were normally positioned at six weeks.
The clinical string check had a high negative predictive value immediately after insertion (NPV 0.98 [95% confidence interval 0.96-1.0]) as well as six weeks later (NPV 1.0 [0.98-1.0]). In other words, if the strings appeared to be the appropriate length, the IUD was in the uterine cavity. The positive predictive value for clinical string check was lower (PPV 0.6 [0.39-0.81] and 0.54 [0.26-0.81], respectively). If the strings appeared longer, that did not always mean the IUD was incorrectly positioned. This supports a strategy of performing a clinical string check first. If normal, no further workup is needed, but if there is concern, an ultrasound might be useful. Interestingly, all the women in this study with an abnormal IUD position at six weeks were symptomatic, which also supports reliance on good history and physical exam skills. No pregnancies were observed.
Is a low-lying IUD still effective?
The IUD is one of the most effective birth control methods available to women. First-year typical-use failure rate is 0.8% for the CuIUD and 0.2% for the LNG IUD, and continuation rates are high at 78–80%. These very low failure rates make it challenging to perform a study with enough power to examine if low-lying IUDs fail more often. This explains the paucity of data and the mostly retrospective and observational data on this particular topic.
Unfortunately, the published studies currently available do not allow us to differentiate what came first: the pregnancy or the IUD dislocation. IUD failure and its relationship to intrauterine location was investigated by Anteby et al.6 A prospective cohort of 100 women had a ML375 IUD placed. Of these, 97 underwent ultrasound 45-60 days post-insertion. They found that 7.2% had an intracervical IUD location. Age and parity did not influence the IUD location. They compared this information to a group of 25 pregnant women with an IUD in place. Of these women, 52% had an intracervical IUD and the rest were intrauterine.
A case control study by Inal et al examined IUD location in 318 pregnant women with an IUD and in 300 controls of non-pregnant women with an IUD.7 Although 64% of IUDs were dislocated in the cases (defined as far from the fundus or arms rotated), only 11% were dislocated in the controls (P < 0.05). Realistically, the only conclusions that can be drawn from these studies are that an IUD is not located in the right place after a failure occurs, but it is unclear if it was in the right place before the failure occurred.
Using a theoretical approach, the copper IUD prevents pregnancy primarily by being spermicidal, while the LNG IUD thickens the cervical mucus, thins the endometrium, has some spermicidal function, and suppresses ovulation in some women. In both IUD types, the mechanism of action is more global in nature, which suggests that the exact location within the uterus should not matter.
Other outcomes of interest are spontaneous uterine expulsion and symptomatic IUD dislocation, since both require re-establishing effective contraception. If expulsion goes unnoted, it might lead to an undesired pregnancy. Spontaneous expulsion of the IUD occurs in 2-10% of users; nulliparity8 and heavy menstrual flow are risk factors. As pointed out above, most women will complain of symptoms such as lengthening of the IUD string, pain, bleeding, or dyspareunia in the case of a partial expulsion (intracervical), and ultrasound has not been shown to effectively predict which IUD will expel.
We recommend leaving the IUD of above-presented patient and counseling her that it is effective. We would further counsel her to return to clinic in case of symptoms, such as pain, abnormal vaginal bleeding, or in if she cannot feel her strings.