Study of fertility signs finds that only 10% of BBT rises occur the day after ovulation

[kristeen]

I found this study, which absolutely blew my mind - it really highlights the variability in the timing of fertility signs vis-a-vis ovulation. Only a minority of participants had an increase in BBT the morning following ovulation. And a sizeable minority of participants (23%) ovulated before their peak in LH (first peak OPK - this is why you hear that it's better to go off first positive).

I thought this was a great example of how much variability there is in fertility signs, and how important it can be to take a holistic view of multiple signs when trying to conceive instead of relying on just BBT, just CM, or just OPK to say "I definitely ovulated CDx."

eta: /@sisi has pointed out a super important qualifier about the BBT results, which is that they count a "rise" as 0.4-0.5 degrees F (0.2-0.3 degrees C). This is a greater rise than is required by FF to give you crosshairs. A more accurate way of putting these results would be that it can take a while for some people to get to that level of a rise, and a "slow" rise is not at all uncommon.

 

[jmueller]

@kristeen this makes me think maybe just having sex every other day forever is the best solution? god that sounds exhausting

(ps, sjogrens and TTC #1 too!!! hi!!!)

 

[kristeen]

@jmueller HEY THERE. Isn't it great having no cervical mucus at all.

 

[jmueller]

@kristeen lol would you believe I didn’t realize the connection between a flare and CM till like...this month? head in the sand over here

 

[fugi]

@jmueller I feel you with the sjogrens, that’s no joke. I hope your taking care of yourself on this journey!

 

[nthanie]

@jmueller This has been my plan. All the sex! Hahaha

 

[jolyn]

@jmueller My work offers access to FertilityIQ which is a website that provides information about fertility from medical experts (from Yale, Stanford,etc.). Basically they said that OPKs can help but measuring your body temperature is kind of useless especially since you only notice a change--if you do at all--after you ovulate. They said that the best advice regarding timing sex is to have sex every other day once your period has ended until ovulation.

So yeah your hypothesis is backed by medical experts!

 

[mcg1102]

@jolyn BBT is useless for prospectively timing sex, it's true, but it's pretty useful for identifying when it's safe to stop having sex, and for knowing when you can expect a period or a positive test. Predicting when ovulation will occur isn't the whole game.

 

[jessicamorris]

@mcg1102 Agree. I was shooting blindly in the dark for the first half of last year, even though OPKs narrowed this window considerably, until I learnt how to track BBT. I'm one of these people the study says has a BBT that rises slowly, over three days. Based on OPKs and temps I know exactly when to test or expect a period (usually 12-13 days after the predicted ovulation day).

 

[halo888]

@mcg1102 Agreed. For me, confirming that I did indeed ovulate when I expected takes so much uncertainty out of the game. The few months I didn't use BBT but only OPKs I kept wondering if we did indeed hit the right days which took way too much mental energy tbh.

 

[ady2015]

@jmueller I also have Sjogren's!

Funny story about that - I had to go to my local hospital's emergency department in December. The doctor had never heard of Sjogren's, and kept spelling it "Showgrins." When he was entering his reports my Medicare/My Health Record online chart, I spelt it as "Showgirls," so all my treating health professionals got a report saying I've been diagnosed with Showgirls Syndrome.

My CM seems pretty normal though, possibly because I'm loaded up with Prednisone, sulfasalazine and hydroxychloroquine? Where I really struggle is natural lubrication during arousal. It's never really existed me for me. It was a relief to be diagnosed and find out that the problem isn't just that I'm bad a foreplay.

 

[jmueller]

@ady2015 Hahaha if only it were just Showgirls!!!!

 

[sisi]

@kristeen This study has been discussed many times and they use an extremely restrictive definition of "temp rise" - it had to be 0.2-0.3 degrees Celsius (0.4-0.5 degrees F) above the average of the previous six temps. That is much more of a rise than FF or most FAM methods require, and means they wouldn't be counting smaller rises. So yes, a delay in rise after ovulation is possible, but not to the extent that the study suggests, since temps tend to follow a bell pattern in the luteal phase and aren't as extreme at first.

 

[kristeen]

@sisi Sorry, I didn't realize it had been discussed before; it is still of interest to me, and I doubt everyone has an encyclopedic knowledge of the sub history so I still think it's worth sharing. Especially for those of us like myself worried about slow temp rises! Good point though about the restrictive definition!

 

[sisi]

@kristeen Yeah sorry, didn't mean to come off as irritable about it! I remember being taken aback by it when I saw it at first, too, but the reading I've done since then has convinced me that you can usually get within ~1 day with charting, though of course the more signs you add (BBT, CM, OPK) to triangulate, the better.

 

[kristeen]

@sisi Oh no you didn't come off as irritable at all! Don't worry! I think your comment was very informative and I'm glad you posted it; it's an important qualifier I didn't consider. (eta: I think communicating tone through text is really hard even in the best of times...)

 

[ady2015]

@kristeen It was also published way back in 2001 - 20 years ago. I looked it up on scholar.google.com and it has been cited by 145 articles since then. I've only skimmed the abstracts for most of them, but I can't see any that have replicated that result. I did, however, find this study published in 2019 with data from over 700,000 menstrual cycles collected in 2018: https://www.nature.com/articles/s41746-019-0152-7

That study found that ovulation occurred on average 12 hours after the first LH surge. As the 2001 study has a teeny, tiny sample size, this study with a massive sample size is a lot more reliable.

There's two reasons a mention this. One is obviously so that people who see this post who aren't familiar with how to browse academic articles don't suddenly think that they're actually ovulating before their surge, and the second is to let you know that Google Scholar's "Cited By" function exists in case you're a tertiary student. I strongly recommend using it for all of your assignments. It'll yield much better quality research results, which will in turn lead to higher grades.

 

[katrina2017]

@sisi Ok...but is it better to err on the side of before peak or after peak?

 

[sisi]

@katrina2017 What do you mean by peak? Peak LH, or peak day of CM? The best days statistically for sex are the 3 days before ovulation day, and they're all about equal, and as long as you hit at least one, you've about maxed out your chances for the cycle and hitting more doesn't really increase them much. Ovulation day itself is lower odds, and the egg only lives 12-24 hours after ovulation (and sperm takes ~7 hours after ejaculation to be capable of penetrating it) if not fertilized, so after is useless. So in general, before is better, but peak LH can precede ovulation by several days (and actually for OPKs it's the first positive, not the darkest, that is most reliable to count from). For peak CM, the last day of the most fertile-type CM is called peak day and is within a day of ovulation for ~75% of cycles.

 

[aster302516]

@sisi

the egg only lives 12-24 days after ovulation

I think you meant to type 12-24 hours after ovulation here...it would be so much easier to hit the fertile window if this was the case!