How do the IUDs prevent fertilisation?

Explanation

**Step-by-Step Solution:**

1. **Definition of IUDs**: Intrauterine Devices (IUDs) are small devices that are inserted into the uterus of females to prevent unwanted pregnancies. They are a common method of contraception.

2. **Types of IUDs**: There are two main types of IUDs - hormone-releasing IUDs and copper-releasing IUDs. Both types have different constituents and modes of action but share some common mechanisms in preventing fertilization.

3. **Thickening of Cervical Mucus**: One of the primary ways IUDs prevent fertilization is by altering the cervical mucus. The IUD thickens the cervical mucus, making it more viscous. This thickened mucus makes it difficult for sperm to move through the cervix and reach the egg, effectively rendering the sperm immobile.

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