This is again from Wikipedia on how to time the "O" period..hope this helps
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Scientific basis
Ova die if not fertilized within 24 hours of ovulation. Ovulation can be detected through changes in basal body temperatures, cervical mucus, and/or cervical position. Once ovulation has passed, conception is not possible for the remainder of the menstrual cycle. Spermatozoa are able to fertilize an ovum for a period of up to five days after they have been ejaculated. If no fertile cervical mucus is present, the acidic environment of the vagina usually results in a dramatically shorter sperm life. Intercourse that occurs more than five days before ovulation is unlikely to result in pregnancy. Intercourse that occurs in the presence of cervical mucus, and/or right before the temperature shift is most likely to result in pregnancy. Most women experience fertile cervical mucus and cervical position changes five or more days before ovulation occurs, giving them sufficient notice to avoid or plan intercourse (depending on their pregnancy intentions).
[edit] Observational methods
This description is an overview only. Couples wishing to use Fertility Awareness to avoid or encourage pregnancy should seek instruction from an experienced teacher.
The three primary fertility signs are basal body temperature (BBT), cervical mucus, and cervical position. A woman practicing fertility awareness may choose to observe one sign, two signs, or, all three.
Basal body temperature is a persons temperature taken when they first wake up in the morning (or after their longest sleep period of the day). In women, ovulation will trigger a rise in BBT between 0.3 and 0.9C (0.5 and 1.6F) that lasts approximately until the next menstruation. Sixty percent of the time, ovulation happens the day before the temperature rise. The other forty percent of the time, ovulation may happen a few days in either direction.
The appearance of cervical mucus and vulvar sensation are generally described together as two ways of observing the same sign. Cervical mucus is produced by the cervix, which separates the uterus from the vaginal canal. Cervical mucus is a heterogeneous mixture of different types of mucus, several of which have specialized functions. Some of its functions are similar to those of semen - cervical mucus promotes sperm life by decreasing the acidity of the vagina and providing nourishment to the sperm. One type of mucus has a structure that helps guide sperm into the cervix and then the uterus. The production of fertile cervical mucus is caused by the same hormone (estrogen) that prepares a womans body for ovulation. By observing her cervical mucus, and paying attention to the sensation as it passes the vulva, a woman can detect when her body is gearing up for ovulation, and also when ovulation has passed. When ovulation occurs, estrogen production drops slightly and progesterone starts to rise. The rise in progesterone causes a distinct change in the quantity and quality of mucus observed at the vulva.[24] Each of the methods of fertility awareness observes and interprets this occurrence differently, and uses different rules to determine the onset of fertility and post-ovulatory infertility.
The cervix changes position in response to the same hormones that cause cervical mucus to be produced and to dry up. When a woman is in an infertile phase of her cycle, the cervix will be low in the vaginal canal; it will feel firm to the touch (like the tip of a persons nose); and, the os the opening in the cervix will be relatively small, or closed. As a woman becomes more fertile, the cervix will rise higher in the vaginal canal; it will become softer to the touch (more like a persons lips); and the os will become more open. After ovulation has occurred, the cervix will revert to its infertile position.
There are other techniques for detecting ovulation. Unlike the three primary signs described above, these other methods are not considered sufficiently accurate to avoid pregnancy. They are often used by couples seeking to conceive.
Ovulation Predictor Kits (OPKs) can detect imminent ovulation from the concentration of lutenizing hormone (LH) in a womans urine. A positive OPK is usually followed by ovulation within 12-36 hours.
Saliva microscopes, when correctly used, can detect ferning structures in the saliva that precede ovulation. Ferning is usually detected beginning three days before ovulation, and continuing until ovulation has occurred.
Fertility monitors are available under various brand names. These monitors use a combination of the calendar method, OPKs, and sometimes computerized interpretation of BBTs. Though the manufacturers claim high effectiveness rates for avoiding pregnancy, independent studies show failure rates comparable to the calendar method.
Many women experience secondary fertility signs that correlate loosely with ovulation. Examples include breast tenderness and mittelschmerz (ovulation pains).
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at least can stop me from thinking whether i preg or not loh..now i know is BFN so these few days can wait for AF to come..if by weekend AF not come..then i gonna think again..lol
