What percent of a woman's cycle is fertile?

The answer to this question is somewhat tricky. The general answer is that most women are fertile for only a few days per cycle. However, there are several factors to consider:

   1. The woman's egg can only live up to 24 hours. Two or more eggs may be released over a maximum of 24 hours. So, in a vacuum, a woman is only fertile for about a day or two. But the man's sperm can live up to 5 days, so the combined fertility of the two individuals is about a week.
   2. For a couple trying to get pregnant, the woman's fertile phase is as long as she has fertile quality cervical fluid, up through ovulation. That might be several days, or as few as one.
   3. For a couple trying to prevent pregnancy, FAM adds a buffer zone of a few days to assure that an unplanned pregnancy does not occur. This usually results in about 7-10 days being considered fertile per cycle.

 
Can a woman get pregnant during her period?

The answer lies in the wording of the question. More precisely, it is essentially impossible for a woman to get pregnant during her period, but on rare occasions it is possible for a woman to get pregnant from intercourse during her period. Since sperm can live for five days, a couple could have sex near the end of the woman's period, and the sperm could then live long enough to fertilize an egg several days later, if the woman had a very early ovulation. (Conception is more likely in these cases if intercourse occurs at the end of a 6- or 7-day menstruation.) It's also possible that women who think they got pregnant from intercourse during their period were actually having sex during ovulatory spotting.
 

Can you be pregnant and still have your period?

It's fairly unusual to be pregnant and still have a normal period. This is because the very thing that causes women to menstruate is the drop in progesterone that occurs only if fertilization does not happen. If a woman were pregnant, her progesterone levels would remain high, thus preventing her from having a period. Of course, there are times when pregnant women do indeed bleed, but by definition, these bleeding episodes are not true menstrual periods:

   1. Implantation spotting: This is usually brownish spotting that occurs in some women about a week or two following fertilization. It is due to the egg implanting in the uterine lining, causing a small amount of the lining to be shed.
   2. Bleeding due to hormonal shifts occurring with pregnancy: In this case, it may be perfectly normal, or it may signal a potential problem requiring a physician's observation.

Then there are the cases where the opposite occurs, in which a woman actually thinks she is pregnant when she really is not. The most common cause of this is when women have a delayed ovulation, which causes them to menstruate later than usual, often leading them to think that they are pregnant because their period is late.

Regardless the easiest way to determine why you are or are not bleeding is to chart your waking temperature. Once you do so, you will probably find that it provides so much valuable information that you'll wonder how you got by while being so unaware.


How long can a human egg survive?

Most ova probably survive about six to twelve hours after ovulation. However, for the purposes of contraception, you must count on a 24-hour survival period, plus an additional 24 hours in case there is a multiple ovulation.

How does the Pill work?

In essence, the Pill works by tricking the body into thinking it's already pregnant. It does this by manipulating the normal hormonal feedback system. The end result is that the body doesn't release the hormones necessary to stimulate the ovary to release an egg.

As a back-up, every other facet of the woman's reproductive system is also altered. The uterine lining is prevented from producing a suitable environment for egg implantation, and the cervical fluid doesn't develop the fertile quality necessary for sperm survival.