The cervical mucus, around midcycle, should  be clear, watery and enough to allow to normal sperm to move towards the uterus and fallopian tubes.

Previous surgical treatment, cryotherapy, cone biopsy or laser therapy, could result in alterations in cervical composition which may cause infertility. Sometimes, even when composition is normal, defective functioning does not allow sperm passage. In some cases , there is an incompatibility between the sperm and the cervical mucus (antisperm antibodies) causing immobilization of sperm thus preventing fertilization.

How cervical mucus defects are diagnosed

The Huhner test (post coital) is used to test the cervical mucus, the sperm and the interaction between them. The test is performed 1-2 days before ovulation and within 20 hours after sexual intercourse. Normally, sperm can be found inside cervical mucus up to 48 hours after intercourse. When defective mucus is considered an obstacle to the normal passage of sperm, antibiotics or hormonal treatment can be given. Also, intrauterine or intrafallopian insemination (GIFT) can be offered.