Role of cervical mucus in human infertility.

The physiological role of cervical mucus in enhancing spermatozoal penetration at mid-cycle has been established. However, the involvement of cervical mucus in primary infertility is still controversial. Although immunological reactions against spermatozoa in the female have been offered to account for the immobilization of spermatozoa--an observation termed 'hostility' of the mucus--this is not always demonstrable. In addition, there are a number of microbial antigens that are similar to spermatozoal antigens. Antibodies to these antigens are found in the serum of the majority of females and males whose infertility is considered to be immunopathological in origin. There are also naturally-occurring antispermatozoal antibodies in both females and males that in some cases may contribute to immunological infertility. The overall spectrum of 'hostile' mucus reactions becomes more complex when we consider the biochemical structure of cervical mucus and its possible interaction with spermatozoa. This spermatozoa: mucus interaction may involve the transfer of spermatozoal components to 'hostile' mucus that should normally be transferred to the zona pellucida of the ova. In addition, there are also pH changes in some 'hostile' mucus that lead to spermatozoal immobilization. In contrast to the above, the cause of infertility in some cases is the inability of spermatozoa to survive in normal mid-cycle mucus. It is evident therefore that an understanding of the complex nature of 'hostile' cervical mucus will lead to a more objective approach in the treatment of infertility.