As you know, having vaginal discharge throughout your cycle is normal. It is also normal when the cervical mucus changes. This is healthy and a sign of hormonal shifts. The volume, texture, and appearance of cervical mucus is regulated by the key female hormone estrogen. As it shifts throughout the cycle, the cervical fluid changes.

Cervical mucus is fluid that the cervix releases into the vagina. Its job is to keep the vagina lubricated and prevent infection. During some days of your menstrual cycle, it serves as a liquid guard for your vagina. 

Vaginal discharge isn't always sperm-friendly, although egg-white discharge provides the ideal environment for sperm. It helps it swim up from the vaginal canal and cervix into the uterus and fallopian tubes to find an egg there. 

When the cervical discharge is watery, thin, and slippery, and appears similar to an egg white, it means that you are fertile.

Usually, you will have fertile egg-white discharge for one or two days before you ovulate.