Cervical Mucus
Fluid produced by the cervix that changes throughout the cycle in response to hormones.
A primary biomarker for nearly every modern fertility awareness method.
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As estrogen rises before ovulation, cervical mucus becomes more abundant, clear, and stretchy, often described as resembling raw egg white. This change facilitates sperm transport. After ovulation, progesterone causes mucus to become thick, opaque, and inhospitable to sperm.