Are we oddly fertile?
November 30, 2010 7:16 PM   Subscribe

Given 'optimal' circumstances, what are the typical odds of conception from a single act of unprotected intercourse?

In this case by 'optimal' I mean around the time of ovulation.

In the course of our relationship, over the last eight years or so, my wife and I have had sex without any form of birth control on a total of three occasions. One was well outside the typical ovulation window, the other two were around two weeks after her period (typically around the time of ovulation) - both of those occasions have resulted in conception.

By 'occasion' in this context, I might mean a two or three 'acts' over the space of a few hours - but only within those few hours, nothing similar in the days before or after.

Our first child was conceived while she was taking hormonal contraceptive pills (as she had done for many years before, with other partners).

I can't find a good source, but this certainly seems to be well outside of expectations... I presume we're just a very fertile couple.

As a bonus question - is it just one of us who is being the powerfully-furtile one, or is there some sort of combined effect here?

The conceptions are not unhappy or unwanted, just not carefully planned. We were rolling the dice on these occasions.
posted by anonymous to Health & Fitness (13 answers total) 1 user marked this as a favorite

It depends on her age, and probably yours too.
posted by amro at 7:23 PM on November 30, 2010

Your question, as phrased, cannot be answered.
posted by halogen at 7:34 PM on November 30, 2010

Agreed. No way to answer this without knowing more details. Most statistics I've seen say that something like 85 out of 100 couples get pregnant within 1 year when using no contraception at all. Calculating the odds of a single act? Nearly impossible without knowing all the factors involved.

The fact that your first child was conceived while your wife was taking the pill doesn't mean she's excessively fertile. She may have missed a pill, may not have been taking them correctly or consistently, may have been taking another drug that altered the effectiveness of the pill, etc.
posted by pecanpies at 7:42 PM on November 30, 2010

There is NO way to answer this question. I would assume that any percentage you encounter via googling is an estimation based on optimal circumstances, but that number hardly carries any weight. You may both be oddly fertile, or just one of you, or neither of you. Let's say you are. Let's say you aren't. Is that changing anything? Either way it isn't advisable to have unprotected sex if you aren't looking for kids, and you shouldn't base your sexual practices on those facts. Let's say you both possess average fertility. Being reminded of that may help you feel a little better after unprotected sex, but pregnancy is still possible -- especially if you're ejaculating inside of her.

You're rolling the dice EVERY time you have unprotected sex. Whether you're willing to take that risk is the question you should be asking yourself, not how likely it is or hypothetically could be.

I don't intend for my response to come across as curt, btw. It's just that people ask this question all the time and there are too many variables and some of it is based on chance.
posted by overyourhead at 7:42 PM on November 30, 2010

I'm not aware of any research that studies the likelyhood of pregnancy on a per-instance basis. The effectiveness of various types of birth control is commonly quoted as a percentage per year. Using no protection is 15% effective citation - that is, 85% of couples will get pregnant within one year if they don't use birth control.

On the other hand it seems like every teenager I've ever heard of getting pregnant has only had sex once, so maybe the odds are higher.
posted by ChrisHartley at 7:47 PM on November 30, 2010

I can't find a good source, but this certainly seems to be well outside of expectations... I presume we're just a very fertile couple.

Well, that's a false presumption. There's no reason not to believe you didn't just chance on the long odds, and honestly, not all that long of odds. People get pregnant on the pill, it happens. The fact that it never happened to her before doesn't mean anything. You had sex two times within a likely window of conception and got pregnant both times? So what? Two is not a very big statistical sample. Basically your data set is meaningless.

Sure there could be biological factors that make you more fertile, either individually or as a couple. The only way to know more about that would be clinical testing. But the evidence you're presenting that you're extra fertile is pretty slim.

Of course if I were you and I were done having kids I'd be taking some heavy duty precautions...

You're rolling the dice EVERY time you have unprotected sex.

Hey, you're rolling the dice every time you have sex, period. Statistics-wise, I recommend vasectomy.
posted by nanojath at 9:52 PM on November 30, 2010

Well, for a friend of mine back during college, the odds were exactly 100%. It was his first time, too. Was forced to marry the girl. Talk about hitting the trifecta.
posted by Thorzdad at 6:20 AM on December 1, 2010

I'm not aware of any research that studies the likelihood of pregnancy on a per-instance basis.

I just went through a nine month insemination process at an infertility clinic, and definitely, there is research on monthly success rates for couples who are trying. And if you're having sex multiple times at ovulation, you might as well say you're "trying" whether or not that is your intention.

The number my doctor quoted to me was ~20% chance each month for healthy, young, normal couples. It was ~15% for the type of treatments I was undergoing. So yes, it is unlikely (~4%) to get pregnant 2 out of 2 times trying, but as others have said, 2 times is far too small of a number to really determine anything. Come back when you have ~12 kids.
posted by Tooty McTootsalot at 7:24 AM on December 1, 2010

I would wager that a presumably young and healthy couple who has sex on two occasions without birth control, each consisting of 2 to 3 vaginal intercourse acts, during ovulation would get pregnant both times. In other words, you are totally normal.
posted by pintapicasso at 7:35 AM on December 1, 2010

it's just anecdata, but yeah, me and my wife did that too.
posted by jrishel at 8:19 AM on December 1, 2010

There actually is research on day-specific probabilites of conception, as well as other impacts on fecundity. This paper is one that I like; the highest entry in table 1 is 38% (although some studies pegged the max as low as 20%); I'm not going to go through and calculate modifications based on age, smoking, etc. If you had sex on the optimal day and 25% was the chance, that you hit 2/2 isn't uncommon at all, about 6%.
posted by a robot made out of meat at 9:43 AM on December 1, 2010

We would need a lot more information (age, medical history, etc.) about you to give you the most accurate answer to your questions. Knowing something simple as your age can change the answer quite a bit. Age plays a huge factor in fertility, especially in women. Women under 25 are estimated to suffer from infertility only 6%. However, for women over 40 there is a 60% prevalence of infertility.

It's awesome you are able to conceive so easily. For some, it's not that simple. For someone who is fertile, you have the ability to reduce your fertility (i.e. birth control, vasectomy, tubal ligation, etc.), but it gets much trickier for those who are unable to conceive to actually increase fertility.
posted by ohohcyte at 10:18 AM on December 1, 2010

With all the modern day science around infertility treatments, you may be forgetting that the vast majority of people throughout time have had no problem having children. Don't go playing the lottery, you haven't beat any odds here.
posted by WeekendJen at 12:33 PM on December 1, 2010

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