Ferning of cervical mucus depends upon:

The Ferning of the cervical mucus is because of the high estrogen content and its DOES NOT diagnose ovulation. Maximum before ovulation and once ovulation happens, the ferning actually reduces and finally disappears due to the high progesterone. This implies that loss of ferning pattern is suggestive of ovulation. Due to the presence of sodium chloride in the mucus under estrogen effect. This fern pattern is also known as Arborisation.