1.   Hanson said sperm usually live in the cervical mucus for a couple of days, during which time they mature and become capable of fertilizing an egg.

2.   Many users of natural family planning methods currently record basal body temperature and the consistency of the cervical mucus to determine how close they are to ovulation.

3.   The hormones in the pill cause a thickening of the cervical mucus, providing something of a barrier to infectious organisms.

4.   The pill lowers the risk of pelvic inflammatory disease, a common problem for teen-agers, by improving the cervical mucus barrier against bacteria.

5.   They release small amounts of hormone that prevent the release of egg and thicken cervical mucus to keep sperm from joining egg.

6.   They also cause changes in the cervical mucus that can make it impenetrable by sperm.