# Unprotected Sex - any reliable odds of pregnancy? **URL:** \ **Category:** Factual Questions\ **Created:** [November 5, 2011, 8:11pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981 "2011-11-05T20:11:28Z")\ **Posts on this page:** 15\ **Page:** 1
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [November 5, 2011, 8:11pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/1 "2011-11-05T20:11:28Z")
It took my wife and I over a year to conceive our first child. We had waited three years into the marriage before stopping birth control. After the first birth. We started trying for child #2. Two and half years latter she conceived again. That must have equated to 150 or so attempts. We all hear about the virgin teenager that gets knocked up the first time she has sex. A great horror story for promoting birth control. I’m sure somewhere it really has happened on the first experience. Are there any reliable statistics for pregnancy after sex? How much of a factor does age play in it? Is it just too random to predict? ---
**Author:** ![rhubarbarin](https://avatars.discourse-cdn.com/v4/letter/r/eb9ed0/32.png) [@rhubarbarin](https://boards.straightdope.com/u/rhubarbarin)\ **Post date:** [November 5, 2011, 8:28pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/2 "2011-11-05T20:28:50Z")
Due to the time frame you describe you had both primary and secondary infertility. If you had gone to a doctor they would have offered testing and possibly, treatments to hurry things alone. If the woman is over 35, doctors will treat you for infertility after 6 months of failing to concieve, because time is so limited. How do you define ‘trying’? Were you just doing things as usual but with no protection? Or were you tracking her ovulation and making sure you were timing sex favorably in order to exploit the 24-hour window every cycle she was actually, technically fertile (assuming she ovulated every cycle, which many women do not)? Timing is very important due to the short life of the human egg. Before and during ovulation is when many women are the horniest, and might be in enough of a hurry to forgo birth control - this was the case in my mom’s unplanned pregnancies and many others IMO. Factors like age, sperm motility, etc are also significant. For example, you could have fertilized many of your wife’s eggs during that time, but they could have failed to sucessfully implant in the uterus; or done so, but died soon therafter due to genetic abnormalities. Early miscarriage is very common and unnoticeable. Statistics from [Wikipedia on infertility](http://en.wikipedia.org/wiki/Infertility): > [@](#): > > Prevalence > [ul] > [li]Generally, worldwide it is estimated that one in seven couples have problems conceiving, with the incidence similar in most countries independent of the level of the country’s development.[_[citation needed](http://en.wikipedia.org/wiki/Wikipedia:Citation_needed)_][/li][li]Fertility problems affect one in seven couples in the UK. Most couples (about 84 out of every 100) who have regular [sexual intercourse](http://en.wikipedia.org/wiki/Sexual_intercourse) (that is, every 2 to 3 days) and who do not use contraception will get pregnant within a year. About 92 out of 100 couples who are trying to get pregnant do so within 2 years.[[6]](http://en.wikipedia.org/wiki/Infertility#cite_note-autogenerated1-5)[/li][li]Women become less fertile as they get older. For women aged 35, about 94 out of every 100 who have regular unprotected sexual intercourse will get pregnant after 3 years of trying. For women aged 38, however, only 77 out of every 100 will do so. The effect of age upon men’s fertility is less clear.[[6]](http://en.wikipedia.org/wiki/Infertility#cite_note-autogenerated1-5)[/li][li]In people going forward for IVF in the UK, roughly half of fertility problems with a diagnosed cause are due to problems with the man, and about half due to problems with the woman. However, about one in five cases of infertility has no clear diagnosed cause.[[7]](http://en.wikipedia.org/wiki/Infertility#cite_note-6)[/li][li]In Britain, male factor infertility accounts for 25% of infertile couples, while 25% remain unexplained. 50% are female causes with 25% being due to [anovulation](http://en.wikipedia.org/wiki/Anovulation) and 25% tubal problems/other.[[8]](http://en.wikipedia.org/wiki/Infertility#cite_note-7)[/li][li]In Sweden, approximately 10% of couples are infertile.[[9]](http://en.wikipedia.org/wiki/Infertility#cite_note-8) In approximately one third of these cases the man is the factor, in one third the woman is the factor, and in the remaining third the infertility is a product of factors on both parts.[/li][/ul] ---
**Author:** ![lazybratsche](https://avatars.discourse-cdn.com/v4/letter/l/ba8739/32.png) [@lazybratsche](https://boards.straightdope.com/u/lazybratsche)\ **Post date:** [November 5, 2011, 8:35pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/3 "2011-11-05T20:35:38Z")
It’s both hugely variable and age dependent. I believe female fertility begins to decline around 30, and declines precipitously towards and after 40. Male fertility is more stable, but there’s still a gradual decline starting in the 30s. There are all sorts of environmental and genetic factors that also add to the variability, meaning that some couples will reliably conceive just about every time she’s ovulating, while others will try for years without success. Unfortunately my google-fu can’t cut through the umpty-hojillion sites on pregnancy to find much actual data… [This](http://www.ncbi.nlm.nih.gov/pubmed/2697833) looks like it might be a good review, but I don’t have access to the full text. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [November 5, 2011, 8:36pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/4 "2011-11-05T20:36:41Z")
That’s it. One month the wife stopped refilling the birth control prescription. We figured a baby would come along soon enough. It was a surprise that it took so long. We didn’t force sex or anything. Just whenever the mood struck. We were just about ready to consult a fertility doctor when she became pregnant the second time. We weren’t really that worried. Several other couples we knew took a couple years to conceive their 2nd baby. She had just turned thirty when we started trying for the first baby. I’m glad we didn’t wait much longer. > [@](#): > > How do you define ‘trying’? Were you just doing things as usual but with no protection? ---
**Author:** ![Lancia](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/lancia/32/17174_2.png) [@Lancia](https://boards.straightdope.com/u/Lancia)\ **Post date:** [November 5, 2011, 8:37pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/5 "2011-11-05T20:37:05Z")
I just need to point out that there is an ad for daycare at the bottom of this thread. Carry on. 😃 ---
**Author:** ![bizerta](https://avatars.discourse-cdn.com/v4/letter/b/3be4f8/32.png) [@bizerta](https://boards.straightdope.com/u/bizerta)\ **Post date:** [November 5, 2011, 8:42pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/6 "2011-11-05T20:42:03Z")
I once read (without having a cite to show you) that 90% of all sexually active women of child bearing age get pregnant within a year. Let’s assume these sexually active women have sex 80 times a year. So, the odds of NOT getting pregnant can be computed as 0.1 = X ^ 80, where X is the odds of NOT becoming pregnant after a random sex. X = 97.2%, so the odds of becoming pregnant after ONE random sex act is about 2.8%. YMMV. ---
**Author:** ![Bartman](https://avatars.discourse-cdn.com/v4/letter/b/779978/32.png) [@Bartman](https://boards.straightdope.com/u/Bartman)\ **Post date:** [November 5, 2011, 9:00pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/7 "2011-11-05T21:00:16Z")
My understanding is that age plays a huge roll in fertility. [This](http://www.socalfertility.com/age-and-fertility.html) suggests that a woman in her 20s has about a 1 in 4 chance of getting pregnant each month that she has unprotected sex regularly (every 2-3 days). And [here](http://articles.sfgate.com/2002-04-30/news/17541319_1_menstrual-cycle-fertility-age-related) is an article that sums up a study that indicated that fertility drops significantly in the 20s and then drops off a cliff after 35. You don’t say how old you and your wife are, but that could be a factor. I have also heard that your late teens are the most fertile years for anyone, but I can’t find a cite for that. There is also a broad spectrum of fertility. One only needs to look at the [Duggars](http://en.wikipedia.org/wiki/19_Kids_and_Counting) who had 19 children in 21 years, to realize that some people are capable of conceiving quite readily. I haven’t been able to find a hard number from a study, but this [site](http://wiki.answers.com/Q/What_are_the_odds_of_getting_pregnant_if_you_had_sex_only_one_time) suggests around an average 3-5% chance of pregnancy per single sexual encounter. ---
**Author:** ![Hello\_Again](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@Hello\_Again](https://boards.straightdope.com/u/Hello_Again)\ **Post date:** [November 5, 2011, 9:01pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/8 "2011-11-05T21:01:13Z")
You can generally see the “failure rate” of unprotected sex by looking at a [comparison chart of birth control effectiveness](http://en.wikipedia.org/wiki/Comparison_of_birth_control_methods#Comparison_table) Contraceptive effectiveness is calculated by “woman-year” that is to say, year of use, not by sexual encounter. The chart indicates 85% failure rate. Thus, after 1 year, 85% of women using “nothing” as birth control, will be pregnant at least once. ---
**Author:** ![aceplace57](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/aceplace57/32/3500_2.png) [@aceplace57](https://boards.straightdope.com/u/aceplace57)\ **Post date:** [November 5, 2011, 9:38pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/9 "2011-11-05T21:38:23Z")
I guess we weren’t that far off on our first child. It took a couple months over a year without protection. That’s pretty close to those studies. We’re in the 15% that took a little longer. Guilt free, unprotected sex is the best anyhow. We wanted a baby and the wife didn’t have to deal with the pills. ---
**Author:** ![EmAnJ](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@EmAnJ](https://boards.straightdope.com/u/EmAnJ)\ **Post date:** [November 5, 2011, 10:13pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/10 "2011-11-05T22:13:11Z")
The question has mostly been answered, but I just wanted to add that once you start thinking about all the things that have to line up in order for a couple to get a take home baby, it’s surprising that the majority of people are able to procreate at all, let alone multiple times! After one year of well timed sex (i.e. I was tracking my cycle and knew exactly when I was ovulating), my husband and I were referred to an RE. After another year of more well timed sex and a few months of Clomid, we moved on to a fertility specialist. She explained that the chances of conceiving within a year is around 20% - 25% per month for a healthy couple where the woman is under 35 and with well timed intercourse. After a year of well timed sex with no success, the chances start to drop rapidly. We were told once we passed the two year mark that we had a 1% - 3% chance of conceiving each month (conceiving only, this doesn’t mean a take home baby). Sounds like you and your wife really beat the odds! Now that we’re almost at four years, I’m sure our chances of conceiving naturally and taking home a baby are essentially zero. ---
**Author:** ![EmAnJ](https://avatars.discourse-cdn.com/v4/letter/e/d2c977/32.png) [@EmAnJ](https://boards.straightdope.com/u/EmAnJ)\ **Post date:** [November 5, 2011, 10:16pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/11 "2011-11-05T22:16:54Z")
> [@Bartman](#): > > I have also heard that your late teens are the most fertile years for anyone, but I can’t find a cite for that. Yes, mostly because they have higher quality eggs too. Two things start to happen as the female ages: her amount of eggs she has diminishes, and the quality of the eggs she has is reduced. The body will use the best eggs first, so a teenager’s eggs are of much higher genetic quality then someone who is in their 30’s. High quality eggs mean less chance that there is something wrong with it, and a better chance that fertilization and implantation occur and stick. ---
**Author:** ![Fish\_Cheer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fish_cheer/32/17179_2.png) [@Fish\_Cheer](https://boards.straightdope.com/u/Fish_Cheer)\ **Post date:** [November 6, 2011, 11:35am UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/12 "2011-11-06T11:35:53Z")
> [@EmAnJ](#): > > The body will use the best eggs first How does it know? ---
**Author:** ![Kimstu](https://avatars.discourse-cdn.com/v4/letter/k/ecd19e/32.png) [@Kimstu](https://boards.straightdope.com/u/Kimstu)\ **Post date:** [November 6, 2011, 11:07pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/13 "2011-11-06T23:07:31Z")
> [@Fish\_Cheer](#): > > > [@EmaAnJ](#): > > > > The body will use the best eggs first > > How does it know? That phrasing is a bit misleading: the thing is that younger women have a higher **proportion** of healthy ova. The average quality of the ova actually declines with age; I believe it’s something to do with the energy available to the mitochondria. So it’s not like your body deliberately selects the best-quality eggs for ovulation in your younger years; rather, there’s a general tendency for the eggs to degenerate as you get older. ---
**Author:** ![Fish\_Cheer](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/fish_cheer/32/17179_2.png) [@Fish\_Cheer](https://boards.straightdope.com/u/Fish_Cheer)\ **Post date:** [November 6, 2011, 11:12pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/14 "2011-11-06T23:12:44Z")
> [@Kimstu](#): > > So it’s not like your body deliberately selects the best-quality eggs for ovulation in your younger years; rather, there’s a general tendency for the eggs to degenerate as you get older. OK, makes more sense that way. Thanks for clearing it up. ---
**Author:** ![md2000](https://avatars.discourse-cdn.com/v4/letter/m/73ab20/32.png) [@md2000](https://boards.straightdope.com/u/md2000)\ **Post date:** [November 7, 2011, 3:06pm UTC](https://boards.straightdope.com/t/unprotected-sex-any-reliable-odds-of-pregnancy/601981/15 "2011-11-07T15:06:53Z")
The important point is that every woman is different. There are 7 bilion anecdotes in this world. I know families with 3 children that started at 40, a woman that had an accident at 38 after only 2 or 3 months. I know a couple that were surprised after 15 years, long after they had given up. There’s only one way to find out whether you can get pregnant. Even if an assist is needed, there’s no guarantee anything will work or how long it takes.