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Effectiveness of barrier method during fertile window

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CharbKM Posted: Tue, Dec 6 2016 2:06 PM

Hi, this is a follow up post to this: http://forums.ovusoft.com/forums/t/278730.aspx

 

i am am hoping someone can help me understand the numbers.  If we are TTA and use a barrier method during the fertile window what is the likelihood of pregnancy? How does it compare to the effectiveness of the barrier method at any time?  remember it being addressed in the Tcoyf book as an increased likelihood but not walking through the numbers.  

 

So so if for example a diaphragm has a 10% likelihood of a pregnancy at any time, but by using unprotected on any day there is a pretty small chance of conceiving because you are only in your fertile window say 30% of the time.  So therefore if there is  a 20% chance of conceiving in any given cycle when having sex during the fertile window, does that mean that the stats work out to be a 50% chance of conceiving by using the barrier method during the fertile window? I think I am missing something here but lack of sleep is making me forget college stats.... would a numbers person please walk me through this?? 

 

Also  I feel like I need to be extra cautious with these stats because I have TTC in exactly two cycles and fallen pregnant both times... I want to add that if a baby were to come we would welcome him or her, but I am trying to understand exactly what risk we are taking 

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justtryingthisout replied on Tue, Dec 6 2016 2:52 PM

If I'm reading the replies on that thread correctly, the original poster was mistaken. Basically, if a diaphragm is 90% effective (I'm making that up!), that means 10% of people using over the course of the year got pregnant. They would not have gotten pregnant if they weren't in their fertile window! So the studied efficacy should apply, even though you are in your fertile window. There is no need to factor in the chance of conceiving in any given cycle, because  that is really already taken care of.

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tmonee replied on Tue, Dec 6 2016 5:46 PM

I wouldn't get too hung up on the actual percentages. Just know any sex prior to confirmed ovulation carries a risk of pregnancy, some days just have more risk than others. I did search a little and found this chart from the CDC:

http://www.cdc.gov/reproductivehealth/contraception/index.htm

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dj rayne replied on Wed, Dec 7 2016 6:45 AM

As tmonee said any day prior to ovulation carries risk. The risk is not the same with some days being riskier than others. The only time there is a pregnancy with any barrier failure it occurred on a day that pregnancy was possible. You don't know the risk until after the fact and O is marked. So you use your choice and use it correctly to see the optimum results. Even then there are pregnancies reported because even with perfect use there is product failure. This would be why many choose to use barriers pre O on the less risky days and totally avoid in the window where O is expected from the increase in signs that say O is coming.

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justasarah replied on Wed, Dec 7 2016 8:22 AM

DJ and Tmonee are right, and I just also wanted to reiterate that it's incorrect to think of failure rates as a percentage chance that the method will fail each time you use it.

Failure rates are how many women over the course of 1 year using a method (having sex in a heterosexual relationship) fall pregnant. The CDC chart copied above appears to use the "imperfect use" numbers for a diaphragm, showing 12 women out of every 100 will get pregnant in a typical year using it. (With perfect use every time, Planned Parenthood cites that the diaphragm failure rate is only 6 in 100.) That does not mean you have a 6-12% chance of getting pregnant each time you use it. 

  • If women always use the diaphragm as directed, 6 out of 100 will become pregnant each year.
  • If women don't always use the diaphragm as directed, 12 out of 100 will become pregnant each year.
  • - See more at: https://www.plannedparenthood.org/learn/birth-control/diaphragm#sthash.LgDqOBfd.dpuf

    (PP source: https://www.plannedparenthood.org/learn/birth-control/diaphragm )

    It has been a while since I read it, but I thought the point in TCOYF was that if you are using FAM and abstaining on fertile days, the failure rate would be whatever percentage - and if you instead use a barrier method of birth control on the fertile days, your failure rate might be higher because, by default, if it did fail, you now have had unprotected sex in your confirmed fertile window (whereas if you were just using a barrier method all of the time without charting/regard to fertile window, sometimes it might fail in a fertile window or sometimes it might fail in an infertile window and would not cause a pregnancy, which is probably why, in the case of a diaphragm, only 6 to 12 women fall pregnant in a typical year). Sorry if that just makes it all more confusing...

    Anyway. As PPs have noted, any sex before confirmed ovulation carries a risk of pregnancy :)  I'm sorry that I can't give you a percentage chance of pregnancy on a per-intercourse basis, but I'd be very wary of any number that purports to do so - there are so many factors and every source I have seen that tries to take the effective rate and parse it into something else skews the numbers.

  • If women always use the diaphragm as directed, 6 out of 100 will become pregnant each year.
  • If women don't always use the diaphragm as directed, 12 out of 100 will become pregnant each year.
  • - See more at: https://www.plannedparenthood.org/learn/birth-control/diaphragm#sthash.LgDqOBfd.dpuf
  • If women always use the diaphragm as directed, 6 out of 100 will become pregnant each year.
  • If women don't always use the diaphragm as directed, 12 out of 100 will become pregnant each year.
  • - See more at: https://www.plannedparenthood.org/learn/birth-control/diaphragm#sthash.LgDqOBfd.dpuf

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    murillo replied on Wed, Dec 7 2016 3:20 PM

    Interesting discussion. I had seen a NY Times article a while back on failure rates extrapolated over 10 years, and it sort of sent shivers up my spine with failure rates skyrocketing across the board as the years go by. According to their infographic, the poorly-labelled FAM (defined in the footnote as the Ovulation method, ie Billings/mucus-only) could expect 94 failures/100 users over ten years. Female sterilization, 5 failures/100 women. You get the picture. http://www.nytimes.com/interactive/2014/09/14/sunday-review/unplanned-pregnancies.html?_r=2

    But then I found this thought-provoking rebuttal http://www.theamericanconservative.com/articles/the-new-york-timess-statistical-contraception-failure/) (Please note I'm just referring to this one particular blog post, not agreeing with the whole blog). Basically, the rebuttal is that fertility is dynamic, not static. Over ten years, there are other factors that change: committed relationships, declining fertility, frequency. Also the extrapolation assumes identical behaviour from people who get pregnant their first year contracepting to those who do not get pregnant. Only that's not true, whether we're talking what the article calls "tipsy sex", irregular cycles, the men in the equation etc.

    So the NY Times extrapolation is flawed. (The rebuttal also noted the coincidence (?) of an article on LARCs in the same edition of the newspaper.) 

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    Ashmariet2005 replied on Wed, Dec 7 2016 4:41 PM

    I read the NY Times article and did not find it shocking. For typical use, it factors in that the woman may not always use the method. I actually thought it made a lot of sense. Can't tell you how many times I've heard someone say they had an accidental pregnancy even though they were on birth control. Once you start talking and find out that they didn't use the method consistently (didn't always use a condom, didn't always take the pill at the same time every day, didn't always make it in time to the dr for the depo shot etc), it's not as shocking and in fact I want to say "DUH" to that person. 

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    murillo replied on Wed, Dec 7 2016 11:45 PM

    Isn't that user failure you described already factored into the Pearl index, though? I guess it's an interesting question whether people get more experienced and careful as they go along, or more jaded or careless. Does the Pearl index look at all types of users, new and experienced, or only people using a method for the first year ever?

    The NYT infographic gave ten-year failure rates of 81 pregnancies in 100 users for condoms, 61/100 for the pill. Very misleading, IMO, on cursory reading, and rather terrifying. That's why the explanation of how fertility is not static made sense to me.

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    CharbKM replied on Thu, Dec 8 2016 7:39 PM

    I agree that article and those graphs are unnerving!  but baby making is not like coin flipping, i agree with the rebuttal....

    I am not trying to quantify the risk perfectly, and of course I do understand there is some risk with pre-O no matter what you do.  I am not trying to figure out if its 11% vs 12% for example. I was more curious if it somehow doubles or triples during the fertile window. 

    This was my logic  - if your "chance" of pregnancy in any given cycle is 20% with sex during the fertile window, and the chance with using a diaphragm is 10% (presumably, spread over an entire cycle), that really means the barrier method only gets you an "extra" 10%.  By definition those 10% of pregnancies must have happened during the fertile window, so using a diaphragm takes you from a 20% change to a 10% chance. But something feels incorrect about this.....  

    On page 125 of TCOYF it says: "The Fertility awareness method works as a contraceptive only if you choose either to postpone intercourse or use a barrier method when you are fertile.  Statistically speaking, though, you should be aware that the method is much more effective if you choose to abstain a that time."  

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    dj rayne replied on Fri, Dec 9 2016 6:40 AM

    The risk is calculated based on the number of pregnancies that occur over a given period of time. That risk can be calculated for perfect use or typical use. As you can only get pregnant when you are fertile, the risk only applies at that point in your cycle. If you are not fertile you have 0% chance of pregnancy and using a barrier or chemical interference is irrelevant, BUT you don't know that before hand. The problem arises because you cannot 100% reliably predict your O date. You can only make that determination after the fact. The closer you are to ovulation the higher the risk. Because sperm have a life of their own and that life is much longer than the egg then a failure even 9 days out could result in a pregnancy. I have seen reports of live sperm in the tubes at even 12 days past sex but I trust those less than the ones from 9 days prior. Total fertility is a combination of BOTH partners. If you absolutely do NOT want a child then you gear your activities to NO risk which means NO sex until O is confirmed. As you move away from that absolute you start bringing in risk and what your comfort level is. You will never be able to determine actual risk just make an educated guess after the fact. The absolute riskiest is sex on your prime day with no barrier or interference with both partners at their prime with healthy reproductive tracts. There is a wide range of risk between the two.

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