Does the 20% chance of conceiving...

elizjane26 · November 2009

.....still apply if you are charting and have good timing? You would think that the percentage would be higher. Is it 20% regardless?

11Lemon11 · November 2009

I think it is 20% regardless, there are a lot of ducks that need to line up for things to become magical.

GL!

Pink22_83 · November 2009

I think it;s 20% regardless. Which is annoying, oh well. There are just SO many factors that can dictate whether you will get pregnant in any given cycle.

Ski&Sail09 · November 2009

My OB/GYN friend said that unless it's a medicated cycle no matter what you do it's 20%. Lame I know.

gymnst1013 · November 2009

11Lemon11:

I think it is 20% regardless, there are a lot of ducks that need to line up for things to become magical.

GL!

I agree. Someone did link an article the other week that said it was greater than 20% but it wasn't nearly enough to convince me.

Jaimie01 · November 2009

There was a debate about this maybe last week. Someone posted a article that said if you were charting and all of that fun stuff your chances were increased. I do not know how true it is but you might be able to find it if you look back.

elizjane26 · November 2009

Ski&Sail09:
My OB/GYN friend said that unless it's a medicated cycle no matter what you do it's 20%. Lame I know.

This actually makes me feel better. My timing has been perfect thus far, and no BFP. If the % were higher, I might worry more.

locash · November 2009

Yea, that article the other week didn't convince me, either. I've always heard the 20%. It sucks to think that someone not trying has the same chance you do with well timed sex.

gymnst1013 · November 2009

LovedByHim316:
gymnst1013:
11Lemon11:

I think it is 20% regardless, there are a lot of ducks that need to line up for things to become magical.

GL!

I agree. Someone did link an article the other week that said it was greater than 20% but it wasn't nearly enough to convince me.

Yeah, I remember that. I think the article said something like 60%.

Yeah, that sounds right and is obviously bogus or we'd all be knocked up right now!

Hyfagal · November 2009

I've heard it's 20% even if timing is perfect so I'm voting yes.

Bridetobe3/07 · November 2009

That sucks!

eab3093 · November 2009

It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

floridakat · November 2009

I think that the idea is any time you have sex during your fertile period, you have a 20% chance of conceiving. If you chart and time well, you can cut down on the number of cycles it will take you (all things being equal), but not actually increase your chances on any one cycle. Does that make sense?

elizjane26 · November 2009

floridakat:
I think that the idea is any time you have sex during your fertile period, you have a 20% chance of conceiving. If you chart and time well, you can cut down on the number of cycles it will take you (all things being equal), but not actually increase your chances on any one cycle. Does that make sense?

Yes.

sarahandeddiejune212008 · November 2009

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

Your chance of conceiving each cycle is still 20% because each cycle is an independent event. One cycle has no effect on another as long as you are healthy.

gymnst1013 · November 2009

floridakat:

I think that the idea is any time you have sex during your fertile period, you have a 20% chance of conceiving. If you chart and time well, you can cut down on the number of cycles it will take you (all things being equal), but not actually increase your chances on any one cycle. Does that make sense?

Yeah, that makes perfect sense.

jteneback · November 2009

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

My doc said 90% of couples will concieve within a year.

eab3093 · November 2009

sarahandeddiejune212008:

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

Your chance of conceiving each cycle is still 20% because each cycle is an independent event. One cycle has no effect on another as long as you are healthy.

That makes sense. It just seems like a 20% chance is so low and I don't see how it ever happens

floridakat · November 2009

Dude, if I had a 20% chance of winning the lottery every week, I'd actually buy a ticket once in a while!

elizjane26 · November 2009

floridakat:
Dude, if I had a 20% chance of winning the lottery every week, I'd actually buy a ticket once in a while!

Good point!

locash · November 2009

eab3093:
sarahandeddiejune212008:

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

Your chance of conceiving each cycle is still 20% because each cycle is an independent event. One cycle has no effect on another as long as you are healthy.

That makes sense. It just seems like a 20% chance is so low and I don't see how it ever happens

Well, it happens 1 out of every 5 times.

And yes, it does seem very low. but it does happen.

hrparker · November 2009

gymnst1013:
LovedByHim316:
gymnst1013:
11Lemon11:

I think it is 20% regardless, there are a lot of ducks that need to line up for things to become magical.

GL!

I agree. Someone did link an article the other week that said it was greater than 20% but it wasn't nearly enough to convince me.

Yeah, I remember that. I think the article said something like 60%.
Yeah, that sounds right and is obviously bogus or we'd all be knocked up right now!

Not bogus.

It's not 100% because, for example, not all of the eggs we release are viable.

Here's the abstract of that article again, and I'll try and find some more reader-friendly articles to post:

J Reprod Med. 1992 Oct;37(10):864-6.
Cumulative pregnancy rates in patients with apparently normal fertility and fertility-focused intercourse.
Hilgers TW, Daly KD, Prebil AM, Hilgers SK.
Department of Obstetrics and Gynecology, Creighton University School of Medicine, Omaha, Nebraska.
Fifty consecutive clients achieved pregnancy using a standardization modification of the Billings ovulation method (the Creighton Model Natural Family Planning System). Of 50 clients followed, 38 (76%) achieved pregnancy in the first cycle of fertility-focused intercourse, 45 of 50 (90%) achieved pregnancy by the third cycle and 49 of 50 achieved pregnancy by the sixth cycle (98%).
PIP: The effectiveness of the standardized modification of the Billings ovulation method of natural family planning in fertility focused intercourse was evaluated in a study over 12 months of 50 clients aged 22-38 years. 27 had prior pregnancy/s. All clients had normal fertility. The results indicated a higher probability of conception when the couple was aware of their peak fertile time than previously expected. No clients became pregnant when intercourse was confined to the infertile period. Within 1 cycle, 76.0% became pregnant. By the 3rd cycle, 90.0% became pregnant. By the 6th cycle, 98% (49 out of 50) achieved pregnancy. 71.4% of those with a prior pregnancy conceived after the 1st cycle. 80.9% of nulligravida women achieved pregnancy after 1 cycle, 89.3% of multiparous women became pregnant after the 4th cycle, and 100% of the nulligravida women became pregnant after the 4th cycle. The method entailed learning about the presence or absence of cervical mucus discharge around the time of ovulation. The beginning of the mucus cycle began with a sticky (a quarter of an inch), cloudy or tacky discharge until the last day when the mucus became clear and stretchy or lubricative. The last mucus was considered the peak day. Clients recorded all acts of intercourse and were assessed at follow-up visits every 2 weeks in the 1st 2 months, and then at 3, 6, 9, and 12 months. The fertile period was defined as the 1st day of mucus discharge through 3 full days past the peak day. Ovulation is considered possible +or- 2 days of the peak day for 95.4% of cycles. Studies of random acts of intercourse show less efficient conception rates. A study by Barrett and Marshall found, by using the Vollman basal body temperature method, that daily intercourse around the period of alleged fertility increased the possibility of conception from 24% to 31% for every 3-4 days to 68% for daily. The WHO fertility figure for the ovulation method in a multicentered trial is 66.7%.

Here's another article that talks about varying rates of conception with timed intercourse. Keep in mind that the 68% is for daily intercourse around ovulation, and this article only discusses rates on various single days leading up to and beyond O day. When you combine the rates for each of those days (and, no, you can't simply add them), you get something closer to the WHO rate of 66 or 67%.

Basically, the point is that the rate is 20% OVERALL. That overall includes people like the GP board who are actively trying and who are charting to find out when they O and having intercourse around the time, as well as random people who have no idea when they O and are just having sex whenever. When you actually KNOW when you O, and plan your intercourse accordingly, your chances of conception increase. If they didn't, why would any of us be bothering with it, kwim?

ETA: The article didn't seem to be working, so here's the results section:

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Probability of Conception around the Time of Ovulation
The couples in this study had intercourse an average of once every three days, a frequency that makes it difficult in most pregnancies to attribute conception to intercourse on one particular day. As a preliminary exploration, we selected all 192 cycles in which conception occurred and examined the patterns of intercourse around ovulation to identify the range of fertile days. In every cycle in which conception occurred, there was intercourse at least once during the six consecutive days that ended with the day of ovulation. There was no shorter span of days that included intercourse in every cycle. Conversely, there were 31 cycles (of a total of 625) in which there was no intercourse during this six day interval, and none resulted in conception.
As a preliminary estimate of the chance of conception on individual days, we identified all the cycles in which intercourse occurred on only a single day during the six day period. On the basis of these 129 cycles (21 percent of the total), the proportion with a detected pregnancy ranged from 0.08 on the first day of the six-day period to 0.36 on the sixth day (the day of ovulation) (Fig. 2).
For all 625 cycles, we applied our statistical model to estimate the chance of conception on each of the six days in the fertile period. These probabilities ranged from 0.10 to 0.33 - figures similar to the proportions for the single-day cycles (Fig. 2). Standard errors for the estimated probabilities are provided in Table 1. The proportion of ovulatory cycles potentially able to produce a pregnancy (cycle viability) was estimated to be 0.37 (95 percent confidence interval, 0.31 to 0.48). We added one day to the six-day period in each direction and repeated the analysis. The estimated probability of conception was zero on both marginal days. However, we cannot exclude a probability of conception of up to 12 percent on either the seventh day before ovulation or the day after ovulation (95 percent confidence interval, 0 to 0.12).
If the cycle is viable (i.e., if conception is possible), the model assumes that each day of intercourse in the six-day period contributes independently to the probability of pregnancy. Thus, daily intercourse would produce the highest probability of conception (0.37). The estimated rate of conception falls to 0.33 with intercourse that averages every other day (assuming no special timing with regard to ovulation). At lower frequencies of intercourse, the rate of conception drops more rapidly; untimed intercourse averaging once per week would produce a 0.15 chance of conception per cycle. Considering live births only (which accounted for two thirds of the conceptions), the approximate probability would be 0.25 with daily intercourse, 0.22 with intercourse every other day, and 0.10 with weekly intercourse. The assumption that each day on which intercourse occurs makes an independent contribution to conception is open to question. Frequent intercourse might decrease the potency of semen - for example, by depleting the number or quality of sperm.
As a rough test of this hypothesis, we sorted cycles according to the number of days on which intercourse occurred during the six-day period. If frequent intercourse decreases the fertilizing capacity of sperm, then the observed number of pregnancies initiated in cycles with more frequent intercourse should be less than that predicted by the combined day-specific probabilities. Similarly, cycles with intercourse on only one day should produce more pregnancies than predicted. Table 2 shows the predicted and observed numbers of pregnancies for each frequency of intercourse (from none to daily) during the six-day period. The model fits well across the range of values for the frequency of intercourse, with no overall trend toward lower fertility with a higher frequency of intercourse. (emphasis mine).

KMS416 · November 2009

floridakat:
Dude, if I had a 20% chance of winning the lottery every week, I'd actually buy a ticket once in a while!

Yes

CityGirl07 · November 2009

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

I confuse myself with this sort of thinking, too. If you have a 20% chance each month, or 1 in 5, then shouldn't most people get pregnant within five cycles? Obviously I realize this is not your typical math problem because there are so many factors and as someone said, each month is an individual event...but still...it's somewhat perplexing!

discobush · November 2009

eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

The math goes like this. If you have an 80% chance of not getting pregnant after one cycle, then you have:

.8^2 = 64% chance of not getting pregnant after two cycles (36% chance of getting pregnant)

.8^3 = 51% chance of not getting pregnant after three cycles (49% chance of getting pregnant)

.8^4 = 41% chance of not getting pregnant after four cycles (59% chance of getting pregnant) . . .

. . . and so on. Thus (and assuming that the 20% figure stays constant for an entire year), you would have only a .8^12 = 7% chance of not getting pregnant after 12 cycles (93% chance of getting pregnant). Hope this helps!

discobush · November 2009

elizjane26:
.....still apply if you are charting and have good timing? You would think that the percentage would be higher. Is it 20% regardless?

I would imagine that the percentage is higher than 20% for those who have good timing and lower than 20% for those who don't, such that the percentage for the population as a whole averages out to 20%. Else what would be the point of charting?

hrparker · November 2009

Paisley4140:
elizjane26:
.....still apply if you are charting and have good timing? You would think that the percentage would be higher. Is it 20% regardless?

I would imagine that the percentage is higher than 20% for those who have good timing and lower than 20% for those who don't, such that the percentage for the population as a whole averages out to 20%. Else what would be the point of charting?

CityGirl07 · November 2009

Paisley4140:
eab3093:
It's 20% and it's depressing. My brain isn't working very well today, but if someone did the math, what is the percentage chance of getting pregnant over a 12 cycle period of time? 20% x 12 is 2.4...but does that mean you have a greater chance during 2.4 random cycles out of 12 of getting KU? I am confusing myself now... MEH!

The math goes like this. If you have an 80% chance of not getting pregnant after one cycle, then you have:

.8^2 = 64% chance of not getting pregnant after two cycles (36% chance of getting pregnant)

.8^3 = 51% chance of not getting pregnant after three cycles (49% chance of getting pregnant)

.8^4 = 41% chance of not getting pregnant after four cycles (59% chance of getting pregnant) . . .

. . . and so on. Thus (and assuming that the 20% figure stays constant for an entire year), you would have only a .8^12 = 7% chance of not getting pregnant after 12 cycles (93% chance of getting pregnant). Hope this helps!

Wow, smarty pants! That's actually really, really helpful and I'm jealous of your math skills. Thanks for explaining! Makes sense.

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Does the 20% chance of conceiving...

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Cumulative pregnancy rates in patients with apparently normal fertility and fertility-focused intercourse.

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