What factors determine whether a partner can feel a copper IUD during sex, and how are IUD strings typically managed to

The short version

A properly placed IUD sits inside the uterus, with only the thin strings hanging through the cervix into the vagina [8][23][66]. The device itself is normally too high and too small to be felt during sex [8][9][23]. The strings are soft, flexible plastic threads that usually curl up high near the cervix, so most partners never feel them at all [15][17][24]. Still, some partners do feel them, and how often this happens varies from couple to couple [5][22][43][63].

When the strings are noticed, contact is usually not painful — think a slight tickle rather than an injury [6][15][68]. The evidence also says there are no recorded cases of penis injuries caused by an IUD during penis-in-vagina sex [73]. Cervical mucus can act like a slippery layer between the string and the penis, which is another reason it often goes unnoticed [65]. A partner is more likely to feel the strings during fingering than during penis-in-vagina sex [69]. Note: the evidence talks about IUDs in general, not copper IUDs specifically.

What determines whether a partner can feel the strings?

• Time since insertion. The strings are stiffer in the first few months, so partners may feel them early on [29][51]. Over time the strings soften and become more flexible, making them much less noticeable [30][45][76].
• String length. Strings cut too short can stick out straight and feel pokey or even sharp to a penis [21][25][72]. On the other hand, a sticking or poking string may also mean the strings are too long or the IUD is positioned wrong [31][50].
• String position. Strings that curl, tuck, or wrap around or behind the cervix are less likely to be felt [18][48][53][75]. Strings resting against the cervix, hiding in a fold of tissue, or stuck up high can be very hard to notice [38][40][60].
• Menstrual cycle changes. The cervix changes position during the cycle, which changes the angle of the strings and can make them feel different [35].
• Couple’s sensitivity. Some partners are more sensitive to the strings, while others never notice them even when the IUD is working correctly [34][43].
• Depth and intensity. A larger penis or more intense sex may reach the strings, but this still should not hurt [67][68].
• Sex position. Certain positions can be more uncomfortable, especially with a smaller uterus and a larger device [28]. Adjusting the angle of the hips can help [64]. IUD use does not generally restrict which sex positions work [70].

When it is a warning sign, not just normal string sensation

Feeling the IUD body itself or hard plastic is not normal and may mean the IUD moved or was not placed properly [8][10][27]. A partner complaining about a pokey string can also indicate that the IUD is positioned incorrectly or the strings are too long [50]. Pain during sex may mean the IUD has moved, was not inserted correctly, or — in rare cases — that the IUD is partially expelled, with its stem felt at the cervical opening [27][71][74]. Perforation of the cervix or uterus is another rare complication that can cause pain during sex [42]. A sudden increase in how much the partner feels the strings may also signal displacement [33].

You should get checked if the strings feel sharp, pointy, or crooked, if penetration of any kind is painful, or if string problems keep happening [52][55][56].

How IUD strings are typically managed to reduce discomfort

• Standard trimming. At insertion, the strings are trimmed so they do not protrude too far into the vaginal canal, but they are usually left long enough for a person to feel them during a monthly self-check [44][58]. As an example, one clinic leaves the strings about 3 cm long, just long enough for them to curl up in the back of the vagina and not poke [26].
• Provider adjustment later. If the strings bother a partner, a healthcare provider can trim them, adjust them, or cut them shorter [31][46][61][77][85]. You should not try to trim the strings yourself — see a clinician instead [46].
• Tucking the strings. Providers may tuck the strings behind the cervix, which is normal and often helps stop them from poking the partner [75]. Some people also curl or wrap the strings loosely around the cervix themselves [1][2][49].
• Condoms. Using a condom can soften the sensation of the strings for the partner [1][3].
• Replacing with longer strings. If trimming does not solve the problem, another option is having a new IUD placed and asking the provider to leave the strings longer — longer strings can actually be less noticeable — or switching to a different method [62].
• Trade-offs of cutting too short. Cutting strings very short can make future removal harder, make self-checks harder, and can even allow the strings to curl up into the uterus [20][47][57][77]. Because of these trade-offs, the provider should decide the best string length [32][47].