Abstract: Devices for detecting hydration of cervical mucus (which is indicative of the course of a female's reproductive cycle) include a detector having a light source, a photoreceptor and a light guide positioned so as to guide light from the light source to the photoreceptor. The light guide includes at least one active surface to be wetted by the cervical mucus. The detector may be planar or curvelinear and may be embedded within a distal sensing head or extend upright therefrom (e.g., so as to somewhat penetrate the external cervical os during use). Most preferably, the light guide is fabricated from a fluorocarbon polymer. For use in vivo, the device will preferably include a proximal handle which allows the user to manipulate the distal sensing head into close proximity to the external cervical os. The handle may include a source of electrical power (e.g.