How Pregnancy Odds Work
This article was written for women
Many of us know someone who has been trying to become pregnant for years but just does not make it. Many of us also know someone who becomes pregnant the first time she tries. And many of know someone who is pregnant and in a panic. The problem for is that becoming pregnant, or remaining un-pregnant, is often a game of chance. The question for individual women has to be, is the pleasure worth the risks? I became sexually active too young, was not finding it particularly pleasurable and spent much time worrying about the possibility of pregnancy. It was not worth it, so I chose not to play the game – heterosexually – for a few years; therefore no risk!
What are your individual chances? We can tell you how to increase or decrease your chances of becoming pregnant. However, we can give you no absolute assurances. The data for the efficacy of contraception is usually given for 100 women who are sexually active for a year. But how do the numbers look for an individual act of sex? Consider that with a regular 28 day period you will be fertile, practically, for about two days while the egg makes its way down your fallopian tubes. Sperm can live effectively for two days in your vagina and uterus. Yes, some have been found up to five days etc., but this is a more realistic figure. So, with a perfectly random (no schedule, no plan, no avoiding your period) sex act, your chances of falling into a fertile period are approximately 3 divided by 28 or about 11%. We also know that only about one-quarter of the time that the egg and sperm are present together does pregnancy occur. So, the 11% chance drops to a little less than three percent. Does that seem like a risk worth taking? In fact many of us have taken that risk and gotten away with it; but others were not so lucky!
If, with these chances you have perfectly random unprotected sex 20 times, you have a more than fifty-fifty chance of becoming pregnant. Put another way, if twenty women at your school/work have unprotected sex on any given day, there is a 50 percent chance that someone will become pregnant.
The reasons that we become pregnant only once out of four times when having sex during our fertile time are many. The sperm can get lost and never find the egg. We also know that the egg is not the passive recipient that was thought in the past; the egg actually has defences that can be used to thwart a sperm. So, just as you may turn a guy down, the egg may refuse a sperm; we know little of how this decision is made by the egg. Alternately (and this is quite common) fertilization may take place but be rejected by your body because it is a “defective pregnancy”. Many pregnancies are rejected (miscarried, spontaneously aborted) without our even knowing our egg was fertilized. One time, in my early twenties, I was nearly three weeks late and then had the nastiest period of my life. It is very likely that an egg had been fertilized, was implanted and then rejected by my body for some reason. Most likely, it was a defective pregnancy in some respect.
But just when you thought you had the probabilities figured out – guess what? The figures used above are for a perfectly random event in a perfectly regular woman. So, what are some real implications of this. Rarely is sex a random event conducted when an alarm goes off. It is more frequent in the late evening than any other time of day. This is because of work or school or other schedules. It is more common on weekends than during the week. Many women avoid sex during their periods. And our cycles of hormones make us more responsive (receptive) at some times than others. The same hormones that control ovulation and the onset of our periods also affect our desire. Surprise, but nature makes us more interested in sex during our fertile times and less interested during our non-fertile times.
I happen to be about as regular as is possible. Every fourth Tuesday I begin to become bloated, irritable and uncomfortable. Every fourth Friday, there it is. It is more common that women vary up to three days - with sooner rather than later being more common. Most are not perfectly regular. Younger women especially tend to be rather irregular with their menses. Because the same hormones that schedule our periods also schedule our ovulation, the less regular your periods, the less predictable your ovulation.
Our perfectly predictable woman above, will have to assume herself to be fertile from the eleventh to the eighteenth day of her cycle. Any of us who are less predictable, need to take a longer time off to avoid pregnancy without other contraception. On the other hand, when we wish to become pregnant, the target can be a moving one. Even when we hit the target, our egg may decide against the sperm available or the egg and sperm combination result in a non-viable pregnancy.
In women trying to become pregnant, the frustrations can be enormous. Fortunately, this is a rather small group. If 100 women have unprotected sex regularly for a year, 85 will become pregnant. In the second year another eight or nine will become pregnant. The remaining six are the ones who will need some help with fertility. The larger problem is unwanted pregnancy. It is estimated that one-half of all pregnancies are unplanned; many of these are also unwanted! Before EVER considering an act of unprotected sex ask yourself whether you can live with the possible consequences!
Whether trying to become pregnant, or trying to remain un-pregnant, by being unprotected you are playing a game of chance. You should do everything possible to stack the deck in your favor, because the results have a major significance in your life.