Morphological selection of human spermatozoa in cervical mucus "in vivo"

Spermatozoa morphology at two levels in the cervical canal was compared, at the external and internal uterine orifices, in samples taken "in vivo" during 21 postcoital tests (P.C.T.s). P.C.T.s with cervical mucus, with Moghissi scores lower than 10 and exo- and endocervical pH less than 7 were excluded. At the upper level of the cervical canal, 12 of the 21 P.C.T. showed more than 5% more normal spermatozoa than at the lower level of the canal (in 5 of these P.C.T. the increase was greater than 10%). Selection for normal heads was seen in 2 and for normal tails in 4. The P.C.T. that selected for normal tails all had greater than 10% abnormal tails at the external orifice. These results confirm that there is some selection of spermatozoa during passage through the cervical canal. Above all, the selection appears to exclude those spermatozoa with defective locomotive mechanisms (abnormal tails), which indicates that the mucus acts as a "passive filter" with selection depending on the spermatozoa themselves in relation to motility.