|MadSci Network: General Biology|
Leonie: In the theoretical 28 day human menstrual cycle, ovulation occurs 14 plus or minus 4 days prior to the onset of the next menstrual cycle (the onset of menstrual flow being considered Day 0). The ovum released from the ovary at ovulation is picked up by the oviduct (Fallopian tube) and transported to the site of fertilization (ampulla, distal 1/3 of the oviduct) within ~12 hours. The ovum can survive from 12-24 hours post-ovulation. Sperm can live in the female reproductive tract approximately 72 hours from the time of ejaculation into the vagina. Therefore, it is generally accepted that there are only 3 fertile days in any given cycle. Those being two days prior to ovulation and one day after ovulation. However, it is sometimes difficult to accurately predict ovulation without the use of daily analysis of blood samples for the hormones associated with ovulation. Ovulation may occur earlier or later than is predicted and the fertile period may advance or delay accordingly. Therefore, one would be pretty safe in assuming that 3 days prior and 2 day after the anticipated ovulation the woman would be considered fertile and all other days would be infertile. I hope this helps!! (Although the above information is correct the "natural rhythm method" of birth control has a very high failure rate, and of course does not protect against STDs.--madsci administrator Erin Cram)
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