Double sodium and potassium sulphates revealed by microprobe analysis in dried cervical mucus: a mid-cycle crystallographic index.

The use of physical techniques such as scanning electron microscopy and microprobe analysis permits the analysis of valuable details of the structure of dried samples of mid-cycle cervical mucus during the period of maximum ferning. From a crystallographic point of view, particular attention was paid to the location, morphology and chemical composition of anisotropic organic sulphate microstructures. As distinct from the isotropic sodium chloride pattern described by Papanicolaou, these appear in a narrow period of time corresponding to the middle of the period of maximum ferning. Anisotropic microstructures were revealed to be tiny isolated crystals or polycrystalline aggregates composed of double salts of potassium and sodium. The potassium/sodium cation ratio, equal to 3/1, was constant in the best specimens. Using a simple polarizing microscope, the detection of anisotropic microstructures may be useful to determine the period of maximum fertility more accurately. In addition, experiments have been carried out in order to determine the relative importance of sulphate anisotropic structures as compared with the whole crystallized surface and to investigate precisely their transience after they appear.