An Intrauterine Device (IUD) is a small, T-shaped piece of flexible plastic that a healthcare provider inserts into the uterus for long-acting, reversible contraception. This device is one of the most effective methods of preventing pregnancy, with a failure rate of less than one percent. Despite its high efficacy, the question of whether an IUD can lead to pregnancy loss is a serious concern. Should the rare event of conception occur, the presence of the device introduces complex risks, including a substantially increased likelihood of spontaneous abortion. This article details the specific risks and necessary medical management when a pregnancy happens with the device still in place.
IUD Mechanism of Action in Preventing Pregnancy
IUDs operate primarily by interfering with the reproductive process before a fertilized egg could attempt to implant in the uterine wall. The two main types, copper and hormonal, achieve this high level of prevention through different but overlapping mechanisms. The copper IUD releases copper ions directly into the uterus, creating an environment that is toxic to sperm. This localized reaction impairs sperm motility and viability, making it nearly impossible for the sperm to reach and fertilize an egg.
The hormonal IUD, which releases the progestin levonorgestrel, works mainly by thickening the cervical mucus. This thickened mucus forms a barrier that physically blocks sperm from passing into the uterus. The hormone also suppresses the growth of the endometrium, making it less receptive to implantation should fertilization accidentally occur.
Elevated Miscarriage Risk When Conception Occurs
While IUDs are highly effective contraceptives, they occasionally fail, and an intrauterine pregnancy begins while the device is still in the womb. In this rare circumstance, the risk of spontaneous abortion, commonly known as miscarriage, is significantly elevated compared to a pregnancy without an IUD. Studies have shown that if a pregnancy continues with a retained IUD, the risk of loss can be as high as 48% to 77%.
This increased rate is due to the IUD acting as a foreign body within the uterine cavity. The physical presence of the IUD interferes with the gestational sac’s development and increases mechanical irritation of the uterine lining. Furthermore, the IUD’s presence often induces a localized inflammatory response within the uterus, which disrupts the environment needed to sustain a pregnancy. This risk is high for both copper and hormonal IUDs, as the physical obstruction and irritation are the main contributing factors to the pregnancy loss. If the IUD is removed early in the pregnancy, the risk of miscarriage is reduced, though it remains slightly higher than the general population’s baseline risk.
Medical Management of Pregnancy with an IUD
When an intrauterine pregnancy is discovered with an IUD in place, medical consultation is necessary to determine the best course of action. The primary decision revolves around whether to remove the IUD or leave it in place, which depends heavily on the IUD’s location and whether the strings are visible. The general medical consensus is to remove the IUD at the earliest possible gestational age if the strings are accessible through the cervix.
Removing the IUD reduces the risk of spontaneous abortion to approximately 20% to 33%, a significant improvement over the 50% or higher risk associated with retention. Although the removal procedure itself carries a small risk of inadvertently causing a miscarriage, this risk is outweighed by the greater risk of complications if the device is left in. If the IUD strings are not visible, removal is more complicated and may require specialized procedures, such as hysteroscopy or ultrasound guidance. Retention of the device is associated with much higher rates of second-trimester loss, infection, and premature rupture of membranes.
Distinguishing Other Pregnancy Complications
The IUD’s presence is also associated with two other serious pregnancy complications that are distinct from spontaneous abortion. The first is ectopic pregnancy, where the fertilized egg implants outside the uterus, most commonly in the fallopian tube. IUDs are very effective at preventing all pregnancies, including ectopic ones, thus lowering a woman’s overall absolute risk compared to using no contraception.
However, if a pregnancy does occur while an IUD is in place, a disproportionately high percentage of those rare pregnancies will be ectopic. Anywhere from six to over 50 percent of pregnancies that occur with an IUD are ectopic, making it the first complication to rule out when pregnancy is confirmed. The second complication is the heightened risk of uterine infection, known as septic abortion, which can lead to life-threatening sepsis. This risk is particularly high if the IUD is retained past the first trimester after conception, underscoring the urgency of medical evaluation and management.