An intrauterine device (IUD) is a highly effective, long-acting, reversible form of contraception. This small, T-shaped device works inside the uterus and is considered one of the most reliable methods, with an effectiveness rate of over 99%. Despite this high success rate, a pregnancy can occasionally occur, and when it does, it requires prompt medical evaluation due to the increased risks involved. The presence of the IUD necessitates a specific and urgent diagnostic and management approach to protect the health of the pregnant person and the developing fetus.
Confirming the Pregnancy and Ruling Out Ectopic Location
The first and most important step upon confirming pregnancy with a urine or blood test is to determine the location of the embryo. This is done immediately through a transvaginal ultrasound scan. While an IUD significantly reduces the overall chance of pregnancy, if conception does occur, the IUD’s presence increases the relative likelihood that the pregnancy is ectopic, or located outside the uterus. An ectopic pregnancy most often occurs when the fertilized egg implants in a fallopian tube, where it cannot survive. This condition is a medical emergency because the growing embryo can cause the tube to rupture, leading to severe internal bleeding. For those who conceive with a hormonal IUD, approximately 50% of these rare pregnancies are ectopic, while the rate is about 15% with a copper IUD. Therefore, immediate ultrasound verification of a pregnancy inside the uterus is a crucial safety measure.
Assessing the IUD’s Role in Pregnancy Risks
Once an intrauterine pregnancy is confirmed, the IUD’s continued presence within the uterine cavity introduces specific risks to the gestation. The physical barrier and inflammatory response caused by the device can disrupt the environment necessary for a healthy pregnancy. When an IUD is left in place, there is an elevated risk of adverse outcomes compared to pregnancies without an IUD.
The most notable risk is a substantial increase in the rate of spontaneous abortion, or miscarriage, particularly in the second trimester. Retaining the device can result in miscarriage rates ranging from 48% to 77%. This high rate is thought to be due to the mechanical irritation and localized inflammation the IUD causes within the developing gestational sac.
Another serious danger is the increased risk of intrauterine infection, such as chorioamnionitis. The IUD string acts as a potential pathway for bacteria from the vagina to ascend into the uterus, which can lead to maternal sepsis and fetal infection. The presence of an IUD has also been associated with a higher likelihood of preterm delivery and premature rupture of membranes later in the pregnancy.
Clinical Decisions: IUD Removal Versus Retention
Following the confirmation of an intrauterine pregnancy, the management of the IUD is determined primarily by whether the device’s strings are visible. The decision to remove the IUD is generally recommended if the strings can be easily seen and accessed through the cervix. Removing the device in the first trimester significantly improves pregnancy outcomes, reducing the risk of miscarriage and serious infection compared to leaving it in place.
However, the physical act of removing the IUD itself carries a small, inherent risk of disturbing the pregnancy and triggering a miscarriage. Despite this risk, the odds of a successful pregnancy are better if the IUD is removed than if it is retained. Early removal reduces the spontaneous abortion rate from the high retention range to a range closer to 20%.
If the IUD strings are not visible, removal becomes a more complex procedure, and the device is often left in place. The strings may have retracted into the uterus as the pregnancy grows, making retrieval difficult. When the IUD is retained, the pregnancy requires mandatory, close monitoring due to the ongoing high risks of infection and preterm birth. While the mechanical presence of any IUD is the main concern, some data suggest that pregnancies with a retained hormonal IUD may have an even higher rate of spontaneous abortion than those with a copper IUD.
Monitoring and Long-Term Outcomes for the Pregnancy
Regardless of whether the IUD is removed or retained, the pregnancy is classified as high-risk and requires prenatal monitoring. Surveillance focuses on detecting any signs of intrauterine infection or the onset of preterm labor. Symptoms such as fever, unusual vaginal discharge, abdominal cramping, or bleeding require immediate medical attention to rule out complications.
If the pregnancy successfully progresses beyond the first trimester, the overall prognosis for the baby is generally favorable. Even after the IUD is removed, the risk of preterm delivery may remain elevated. If the IUD was retained, it will typically be expelled from the uterus along with the placenta during or immediately following delivery.