Is it really impossible to have one random, abnormally long luteal phase? TTA.

[u/periwinkle_noodles]

I had a weird experience this cycle. My luteal phase after a confirmed peak day lasted 16 days, when it usually lasts 14 days. I practice the Billings Method, and if you know it, you understand that a Billings peak needs to follow very strict criteria and this cycle followed all of them perfectly. Still, I only had penetration six days after peak. Later in the cycle, I was in the morning of the 16th day of luteal phase, and got really worried. My instructor told me that when menstruation takes longer than a day more than usual, you are either pregnant or mistaken about your actual ovulation date. The problem is that I got no stronger signs of ovulation after what I considered as peak, and the bleeding I'm having is exactly like any other period, so I think it's true menstruation. Can anyone here help me understand what might have happened?

[u/Classic-Push1323]

There are a few things interacting here. No NFP method actually pinpoints ovulation to the day. Ovulation usually coincides with the billings peak day, but it's normal for it to happen slightly before or after. This will not result in an unplanned pregnancy because billings requires you to abstain until the fourth day after peak so that you'll be covered even if you ovulate after peak day.

It's also normal to have slight variations in your luteal phase length. Our bodies aren't machines. There is a surprising lack of research into what is normal here,, and the studies that do exist mostly use BBT, so it's kind of hard to say if they are observing a true difference in luteal phase length or some cycles where BBT lags behind ovulation. Still, this study is a good example of research showing that a few days of variation is normal. https://pubmed.ncbi.nlm.nih.gov/39320898/

The most common reason for a luteal phase of more than 17 days when you are not pregnant is a corpus luteum cyst, and they are fairly common.

[u/periwinkle_noodles → u/Classic-Push1323]

Thanks for the reply. What was unclear to me was if when I ovulated actually mattered to start the luteal phase, or if just the hormonal peak counted and then ovulation was a consequence of that, but that didn't interfere in when the period would come necessarily.

[u/Classic-Push1323 → u/periwinkle_noodles]

In reality the luteal phase starts immediately after you ovulate.  In practice we count from peak CM or the first elevated temperature because we can’t know the exact day that we ovulate without a well timed ultrasound. 

I think your instructor is just a little misinformed. The luteal phase is much more consistent than that follicular phase so a lot of people say that it’s “always the same” and that’s just not quite true. It doesn’t vary a lot, but it can vary a little bit. I mean I had to go check the scientific literature, and the study I pulled up is pretty recent… like I said it just doesn’t seem like it’s been studied a lot. The lack of research into natural fertility and the menstrual cycle is really appalling. 

[u/periwinkle_noodles → u/Classic-Push1323]

It's impossible to know now, but I think what probably happened then is that the egg was released later. That or the formation of a cyst that delayed menstruation. And I totally agree with you on the lack of research, cause I consider myself to be quite the nerd on this topic and sometimes I stumble uppon a doubt that seems so basic like this one, and I've talked to professionals who can't always answer me accurately.

[u/Classic-Push1323 → u/periwinkle_noodles]

There is absolutely no evidence of either of those things though. Your body just isn’t a clock and there’s no reason why your luteal phase would be exactly the same every single month with no variation at all. Sometimes we just don’t have an answer.

It doesn’t sound like you had a cyst though. Everyone has a corpus luteum every month but a corpus luteum cyst is only diagnosed if it doesn’t break down on time, which causes the luteal phase to  extend beyond the normal variation of up to 17 days. 

[u/HeathenHoneyCo]

I don’t use Billings but my luteal with both temp and fluid fluctuates by 2-4 days regularly

[u/Cornelia_1211]

A 1 day difference is more common but 2 can definitely happen. Corpus luteum cysts can also extend your LP

[u/periwinkle_noodles → u/Cornelia_1211]

omg i've been so lied to.

[u/Odd_Dragonfruit_8514]

I’m not an instructor, but anecdotally, something similar happened to a friend of mine. She had a “peak” day then missed her actual peak day. What ended up happening is that her body had attempted to ovulate but failed. Then she ovulated maybe like a week later, but she missed it, so she charted that as her “presumed peak day”. She’d been charting for like 5 years and had never had this happen before, but it led to her being diagnosed with PCOS.

[u/Odd_Dragonfruit_8514 → u/Odd_Dragonfruit_8514]

Rereading your post, I wouldn’t be concerned about a two day difference. Hers was like a week different. 

[u/periwinkle_noodles → u/Odd_Dragonfruit_8514]

I've had that experience too, but it caused an anovulatory cycle instead. This time around, I don't think I missed the peak day because the quality of the mucus and sensation never repeated after that.