Statistically speaking, if a healthy, normal couple has sex (no birth control – not even pulling out) one time on a random day of the month, how likely is a pregnancy?
I would’ve gotten away with it, too, if it weren’t for those meddling kids!
I’m not sure of the exact odds, but it is inversely proportional to the need to remain unencumbered by kids for any period of time.
Tom~
OK, I’m basing this on a site with info on the rhythm method. The easiest and simplest way to do this is to assume the absence of external factors, i.e. the timing of ovulation is the only factor. So my caveat is this this is a highly simplistic exercize.
Simply put, the odds that a woman can get pregnant are the odds that she ovulates while viable sperm are in her body.
An ovum can only survive 24-hours without being fertilized. However “sperm-cells are able to fertilize an egg-cell for a period of about three days after they have been ejaculated, although exceptional cases of fertilization almost one week after intercourse have also been reported.”
So out of an average 28-day menstrual cycle, it would seem that she could get pregnant from sperm that was deposited as far back as week prior to ovulation.
Since the window would be seven days out of 28, I’d say that using this simplified model, at most, the odds of pregnancy are 1-in-4 (25%). This is assuming an average menstrual cycle and sperm with an unusually strong will to live.
Remember when your dog ate my goldfish, and you lied and said I never had a goldfish? Then why did I have the bowl, Bart? Why did I have the bowl?
I just realized how condescending this sounds. I know we all know this, I was just phrasing it in a way that led to the progressive formulation of my little math problem. 
But that 25% must then imply dead certainty during the fertile window, given the residence of viable sperm. Is that realistic, simply based on the stipulation of “healthiness”?
Ray (Asked under the condition of pure ignorance.)
You’d have to figure in that a woman doesn’t always get pregnant if she has sex when she’s ovulating. If you haven’t noticed, plenty of women don’t get pregnant during that time.
Thus, the adds she would get pregnant from having sex at anytime during the month is pretty low. I see that in practice a lot
Well, when you are trying to have a baby, the odds are 95% against your getting pregnant. When you are not trying, the odds are 95% in favor of conception 
“I should not take bribes and Minister Bal Bahadur KC should not do so either. But if clerks take a bribe of Rs 50-60 after a hard day’s work, it is not an issue.” ----Krishna Prasad Bhattarai, Current Prime Minister of Nepal
If I remember dem charts from high school, the yearly chance of getting pregnant from normal sex was between 95% and and 98%. Assuming this means sex every other day we take the 180th root of .02 and .05 and we end up with a chance-per-incident of between about 1.5% and 2.5%.
“If I remember dem charts from high school, the yearly chance of
getting pregnant from normal sex…”
So you can get pregnant from abnormal sex? do tell us that too Konrad.
Yeah, you know, them non-missionary positions & all…
Sue from El Paso
Experience is what you get when you didn’t get what you wanted.
I mean, obviously, that oral and anal sex don’t count.
Of course, handy is proof that even anal sex can lead to pregnancy.
Feel free to ignore that last part.
Has there ever been a study on that? I wouldn’t trust statistics for this application, nor do I trust them for many other situations that have so many variables. I mean, me and my wife would have unprotected sex and she did not get pregnant for about 3 years, on the other hand, many years ago I met a girl who got pregnant two times consecutively… meaning she had sex, got pregnant, the very next time she had sex, got pregnant again.
“Wow! Spider-Man! Are you really friends with the X-men?”
"Not since Cyclops tried to use my viewmaster."
(Marvel Team Up #1)
I’m not asking because I’m planning on having unprotected sex, I’m just curious. It’s a hypothetical.
I would’ve gotten away with it, too, if it weren’t for those meddling kids!
As a form of gambling, you are pretty likely to win/lose, depending in the desired outcome.
We have four girls out of 10 in our office that are pregnant right now… They all claim not to have sex, so the rest of us wont sit on their chairs…
We are, each of us angels with only one wing,and we can only fly by embracing one another
Many, many moons ago, my college Biology book stated that the odds of virgin getting pregnant the very first time she has sex is somewhere around 214,000:1.
How is this pertinent to the subject? It isn’t, it is just statistics and we all know about stats . . .
“Quoth the Raven, ‘Nevermore.’”
E A Poe
Konrad, use the edit button…
“Many, many moons ago, my college Biology book stated that the odds
of virgin getting pregnant the very first time she has sex is somewhere
around 214,000:1.”
Great line. I got to remember that one when I have a new girl around. But of course the chances of getting HIV from unprotected sex the first time is around 1 in 250 still, isn’t it?
If a virgin has sex in the forest, and nine months later, the guy says the kid isn’t his, does the falling tree have to pay child support?
The trouble with Sir Launcelot is by the time he comes riding up, you’ve already married King Arthur.
All of this makes my eyes hurt!! I probably should not have scrolled when reading.
What? Me worry?’