ferning

A term used to describe the pattern of arborization produced by cervical mucus, secreted at midcycle, upon crystallization, which resembles somewhat a fern or a palm leaf.

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n.

a test to determine if the amniotic membrane surrounding the fetus has ruptured in late pregnancy. A typical pattern of amniotic fluid crystallization occurs when the amniotic fluid dries.

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fern·ing (furnґing) the appearance of a fernlike pattern in a dried specimen, due to the presence of sodium chloride and other electrolytes. In a specimen of cervical mucus this indicates the presence of estrogen that is not being counteracted by progesterone. In a specimen of vaginal fluid not contaminated by cervical mucus, it indicates the presence of amniotic fluid.

Ferning of postovulation cervical mucus.