An intrauterine device (IUD) is a small, flexible form of long-acting, reversible contraception placed inside the uterus. These devices are highly effective at preventing pregnancy for several years, making them a popular choice worldwide. All IUDs share a fundamental design but fall into two distinct categories: hormonal and copper. Each type has a unique visual appearance and mechanism of action.
Shared Structure: The Basic T-Shape
All IUDs share a common T-shape framework designed for secure placement within the uterine cavity. This structure consists of a vertical stem and two horizontal arms extending from the top. The T-shape maximizes contact with the uterine walls and anchors the device high inside the uterus.
The core structure is typically made from flexible, medical-grade plastic, such as polyethylene, which is generally white or clear. The horizontal arms fold downward during insertion to pass through the narrow cervical canal. Once inside the uterine cavity, these arms spring back open to secure the IUD against the upper walls.
Two thin retrieval strings, often made of nylon, extend from the bottom of the vertical stem. These strings are trimmed after insertion and rest near the cervix. Clinicians use the strings to confirm placement and to remove the device when its effectiveness period is over.
Appearance of Hormonal IUDs
Hormonal IUDs house their active ingredient, a synthetic progestin called levonorgestrel, within the device. The vertical stem is noticeably thicker than the arms and base because it contains the hormone reservoir. This reservoir typically takes the form of a cylindrical sleeve or capsule, often appearing white or slightly opaque against the plastic frame.
The hormone sleeve is engineered to release a continuous, low dose of progestin directly into the uterus over its lifespan. The plastic frame is usually smooth and uniform in color, typically white or translucent, with no visible metallic elements.
Devices like Mirena and Liletta are generally larger, constructed with a wider profile to accommodate a full hormone dose. Smaller options, such as Kyleena and Skyla, have a narrower and shorter T-frame. These smaller dimensions correspond with a lower overall hormone dosage and a more slender reservoir sleeve.
Appearance of the Copper IUD
The copper IUD is the only device that incorporates a metallic element directly into its design. This type is hormone-free, and its contraceptive action comes from the presence of pure copper. The plastic T-frame is typically a solid white color, contrasting sharply with the metal.
The most prominent visual feature is the fine copper wire tightly coiled around the entire length of the vertical stem. This wire is the source of the copper ions that prevent pregnancy, and smaller bands of copper are often placed on the horizontal arms to maximize the metal’s surface area.
The metallic wrapping on the stem gives this section a textured, non-smooth appearance, unlike the seamless sleeve of the hormonal IUD. The copper IUD (Paragard) is often the largest of the common IUD options, featuring a wider and longer T-shape than most hormonal devices.
Real-World Size and Scale
The actual size of an IUD is small. The largest devices, like the ParaGard copper IUD, measure approximately 36 millimeters (mm) in height and 32 mm across the horizontal arms. This means the entire device is only slightly larger than a quarter coin in height.
Smaller hormonal devices, such as Kyleena, have dimensions closer to 28 mm by 30 mm, comparable in size to a standard paperclip. These devices are designed to fit within the small, pear-shaped uterine cavity, where a difference of only a few millimeters is a significant design factor.
The plastic arms of all IUDs are flexible, allowing them to conform to the contours of the uterus. This small scale and material flexibility ensure the device remains safely anchored within the body.