When trying to get pregnant, how long is our window of opportunity?

Jane Forester

If you're trying to conceive (TTC), you probably wonder when is your most fertile time -- and how long does that "magic moment" last? Family Physician Jane Forester has some information for you.

Your question
When you're trying to get pregnant, how long is the "window of opportunity" in terms of conception? How long can the egg live, and how long can sperm survive? - Joyce in Englewood,Colorado

The expert answers
To determine your "window of opportunity" for conception, you must individualize your own menstrual cycle.

For several months prior to wanting to conceive, you need to track your length of menstrual cycle. Whether 24 or 32 days, it doesn't matter regarding fertility, it just helps with planning. Besides the easiest way to determine ovulation, which is with an ovulation predictor kit, you can also count backwards by 14 days from your period and that is a close approximation to your ovulation date. So in a 32 day cycle, that would be day 18. This information is then useful in subsequent months.



Now for some more facts and more planning. The date of ovulation has a small variation with each menstrual cycle. The hormone called LH (leutenizing hormone) is what triggers ovulation and helps prepare the lining of the endometrium for implantation. Many infertility concepts are based on tracking the LH surge, since this heralds the release of the egg, and is your fertile period. The average egg lives only 24 hours, so it needs to be quickly after its release from the ovary. If an ova is to be fertilized, it is usually within 12 hours of ovulation, so the sperm must be ready. The average male ejaculate contains 200-300 million sperm, 60-90% are physically normal -- fewer than 200 of these sperm even get close to the egg, and only one sperm fertilizes the single egg released at ovulation. Sperm can live up to 72 hours once ejaculated. Sometimes the egg is found within 45 minutes for fertilization, while sometimes it can take as long as 12 hours. If the egg isn't yet released from the ovary, it is thought that the sperm can go into a holding pattern for about 24-48 hours while awaiting release of the egg.

In general, if conception is going to happen in any given cycle, it will probably be within the first few hours after intercourse. The plan of attack to achieve pregnancy is to have intercourse starting every other day after the completion of your period. This would assume with a seven day period, intercourse would take place on days 9, 11, 13, 15, and 17. Normally you can rest assured that this method best increases your chances for pregnancy in any given cycle, barring any other factors suggesting either a male or female factor preventing pregnancy to easily occur.

Best of luck trying, and remember -- try to have fun!

Jane Forester
Family Physician
Glencoe, Illinois