ANALYSIS OF PREOVULATORY 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 a nd 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 sper m penetration of the mucus. Cervical mucus was studied for 12 cycles i n 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 meas urement of both water content (hydration) and penetration by spermatoz oa from fresh specimens of normal human semen. For the latter, a new m icroscale assay was developed and applied, which was amenable to very small volumes of mucus. The new technique determines objective measure s of both the numbers of penetrating sperm (motile and non-motile) and the distance penetrated by the forwardmost vanguard sperm. In these e xperiments, 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 amon g women, with preovulatory baseline levels ranging from 93.8-96.5%. Al l normal cycles (as defined by endocrine profiles) displayed a signifi cant increase in hydration over a one-day period occurring 3-4 days be fore the LH peak. The magnitude of this shift varied among women betwe en 2 and 3% (absolute hydration), a distinction well within the precis ion of the hydration assay. This quantum increase in hydration was mor e 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 cha nges in reproductive hormones. There was a strong but non-linear corre lation 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) whi ch preceded the quantum jump in hydration - which, itself, preceded th e surge of LH. Hydration began to increase approximately 2 days before measurable increases in sperm penetration of the mucus in vitro. Thes e 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 la rge periovulatory and very small samples of collected mucus.