Analysis of pre-ovulatory changes in cervical mucus hydration and sperm penetrability

Changes in cervical mucus occur during the proliferative phase of the menstrual cycle and are known to correlate with receptivity to sperm and to the endocrine milieu. Prior studies, however, have often lacked biological incisiveness and technical objectivity and precision. This study analyzed daily changes in mucus water content (hydration) prior to the LH surge (LH+0) in normal women, in relation to daily levels of serum LH, FSH, estradiol and progesterone, and to daily tests of sperm penetration of the mucus. Cervical mucus was studied for 12 cycles in 10 ovulating women. Three to ten mucus specimens were collected per cycle, over the days LH-8 to LH+0. Each specimen was subjected to measurement of both water content (hydration) and penetration by spermatozoa from fresh specimens of normal human semen. For the latter, a new microscale assay was developed and applied, which was amenable to very small volumes of mucus. The new technique determines objective measures of both the numbers of penetrating sperm (motile and non-motile) and the distance penetrated by the forward most vanguard sperm. In these experiments, variations in semen quality were controlled by performing a companion penetration assay in an artificial 1.5% polyacrylamide gel. The patterns of change in mucus hydration varied quantitatively among women, with preovulatory baseline levels ranging from 93.8-96.5%. All normal cycles (as defined by endocrine profiles) displayed a significant increase in hydration over a one-day period occurring 3-4 days before the LH peak. The magnitude of this shift varied among women between 2 and 3% (absolute hydration), a distinction well within the precision of the hydration assay. This quantum increase in hydration was more pronounced than the corresponding increase in serum estradiol on the same day. The change in mucus hydration, and the associated increase in sperm penetrability, were more consistent among cycles than the changes in reproductive hormones. There was a strong but non-linear correlation between mucus hydration and sperm penetrability. Once the value of hydration rose above approximately 97.5%, there was a substantial increase in penetrability. This 'cut-off point' in sperm penetrability was in the middle of the range of hydration values (across women) which preceded the quantum jump in hydration-which, itself, preceded the surge of LH. Hydration began to increase approximately 2 days before measurable increases in sperm penetration of the mucus in vitro. These results demonstrate that mucus hydration may be a valuable marker of the approach to ovulation and delineation of the fertile period. They also provide new methods for assessing sperm penetration into both large peri-ovulatory and very small samples of collected mucus.