Hormonal coil

The hormonal coil is made of soft plastic and contains only progestogen. It is approx. 3 cm long and is placed inside the uterus. The two threads of the coil come out through the cervix. You may feel these threads by placing a finger deep into the vagina. They are there to indicate that the coil is in place, and to make it easier to remove it later.

Hormonal coils contain a low level of hormones that are released into the uterus. This thickens the mucus in the cervix to stop sperm from reaching and fertilising the egg cell (ovum). Egg cells and sperm cells also become inactive due to the hormones released from the coil.

Bleeding when using the hormonal coil 
Most people who use the hormonal coil experience little or no bleeding. However, some may have regular or irregular bleeding. The bleeding may be a nuisance, but it is not dangerous. 

Different hormonal coils
There are four types of hormonal coils. Mirena and Levosert both last for six years. Kyleena lasts five years, and Jaydess lasts three years. There are only minor differences in the number of hormones they contain. All of these coils can be used by women who have not given birth.

Source: Sex og samfunn