In addition to helping you narrow down your best “go to days” of your cycle, in turn giving you a better chance at making a baby, charting your BBT pattern for just a few cycles can tell you about more than a temperature pattern. Women with lower follicular phase BBTs could possibly have a thyroid that is not functioning properly. If your BBT stays elevated past the first day of your period, there is a chance you could have endometriosis. You do not have to take your BBT every morning to get pregnant, but it is a useful tool to have in your TTC kit!
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What Is BBT and What Makes It Rise Around Ovulation?
Your basal body temperature (BBT) is your lowest body temperature at rest. In women, this temperature changes throughout the month according to which hormones are dominant. After your follicle ruptures and an oocyte comes out, the follicle turns into an organ-like structure called the corpus luteum (CL), or “yellow body” because it is actually a yellow color!

The CL has the important job of producing progesterone and estrogen until an embryo’s placenta takes over hormone production. If no pregnancy occurs, the CL dies and is reabsorbed, thus shutting off hormone production. This signals to the uterus that it can release the endometrial lining because it was not needed to sustain a pregnancy (Steward).
If you take your BBT every morning of your cycle, you will see that when charted on a graph, your temperature has a biphasic shift around ovulation (see graph below). Bi-phasic means “two-phases”. The follicular phase is the first of the two phases, and the luteal phase is the second.

During the first phase of your cycle, your temperature is unaffected by progesterone. After ovulation, the CL begins creating progesterone. In the second phase of your cycle, BBT sees a shift up by 0.5 – 1.0 degree F because of the affect progesterone has on our thermoregulatory system. If you are not at all familiar with charting your BBT for ovulation purposes, you can check out this link from the Mayo Clinic for more information.
Does Ovulation Always Happen on the Nadir?
Garcia studied the prediction of ovulation in 71 cycles by correlating specific guidelines, including evaluation of BBT. The first column of guidelines is labeled BBT dip which is another term for nadir, or the lowest recorded BBT in the peri-ovulatory period. In 46 of the 71 cycles, the nadir occurred on the day of the LH peak. In other words, in 65% of cycles, ovulation took place the day after nadir. In 15% of cycles, ovulation took place one or two days after nadir (Garcia).

Mouzon analyzed 38 cycles for the BBT curve and estimated time of ovulation. His results showed the nadir was usually located before the LH peak, and the first BBT rise occurred about 8 hours after ovulation. In a whopping 94% of the cycles analyzed, ovulation occurred more than 24 hours before the BBT rise (the first high number after nadir). Mouzon found the nadir occurred within the peri-ovulatory only about 25% of the time (Mouzon, download PDF below).
Can’t We Lift Each Other Up a Little?
I’m going to tell a quick story about some mean ladies before I discuss why BBT can be important to monitor. A couple of cycles after I started using BBT for tracking ovulation, back in 2018, I thought I might be pregnant (I woke up with one sock off so of course I thought I could be pregnant, duh!). I tested with a blue dye test (I didn’t know the damn rules about blue dye tests!). After the test dried, I saw a very thin, blue line so of course I got a little excited! I found an online TTC community and got up the courage to create my first post to ask other women what they thought of my “line”.

I was shocked to receive some pretty rude comments about my charting methods and about my awareness of my own body. Also, some women were very skeptical of me ovulating on CD11. I felt somewhat attacked. I felt like an alien. Is that what “support” looks like? I felt even worse.
One year later, I was so alone and depressed that I ended up making a thread for women over 40 TTC. Almost 30,000 comments later and lots of BFPs and take home babies (THBs) made in that group of women. I love those ladies <3. It is my goal to create that same environment here.

(For those interested, I have installed a forum plugin here on my website so we can start chats. The link is in the navigation menu found on each page. Any woman over forty, or close to it, is welcome to register and we can start topics of interest… I’ll make a few topics and see what happens <3)
Seriously, after that incident, I referred to those women as “BBT Nazis” because they adhered to a strictly enforced book of BBT “rules” guarded by a unicorn or some crap. If you question one of the rules, it’s grounds for public slandering. I just so happen to be a master rule questioner.

I cared about BBT in the beginning because I needed all the information I could get as to when ovulation was occurring. Making a baby wasn’t happening right away, that’s for sure. I had not yet started triggering each cycle with HCG. Thank you, Jesus, for the gift of knowing you will ovulate within a 36 hour window! If you ever get tired of getting a shot in your ass-hip, remember our unfortunate wise sisters whom do not get triggered and who have a difficult time pinpointing ovulation. Not a pretty thing.
In February or March, 2019, I started having left-sided pain during my luteal phase. It was down low and it had me worried. This is a sequel, of sorts, to last post’s story. If you remember, I had an ultrasound that showed a CL cyst had already formed by 9am on that particular CD12. I had gotten a +OPK around 4pm on CD10 and ovulated sometime on CD11. What threw me for a loop was that I did not get a temp rise until CD13, two days after ovulation. I thought you got a temp rise the day after ovulation because that is what I was repeatedly told.

This didn’t have me too worried about my own sex schedule, but it got me thinking about the accuracy of the advice given in groups and forums. At our age, not many of us are lucky enough to find an RE who wants to bend over backwards to get us our 4th take home baby with as much gusto as we do! It seems like people have less empathy for older women TTC, especially women whom have children already.
How Can Charting BBT Help Couples in their Forties TTC?
I made up two scenarios that demonstrate how charting could help you out. I am in no way saying you won’t have success if you do not chart, but it can help you when you are first starting out. Heaven forbid you end up like me where two years goes by and you are still trying. At that point, you are happy for any information you have! I don’t judge, but if you do not have regular sex during your fertile period, you might want to listen up.
Example 1) Bonnie and Clyde
Bonnie is 43 and her husband, Clyde, is 48. Clyde has lower counts and his sperm are a little slow… and sorry, Clyde, but your sperm die a bit quicker than your 35 year old counterparts. Bonnie got her +OPK on CD11 and assumed she would ovulate the next on CD12. The couple was busy the evening of CD12 so they planned to have sex CD11, day of +OPK and call it good (obnoxious alarm noise inserted here!).
If your partner isn’t Thor, you cannot have sex one time, the night of +OPK, and call it good. Bonnie was unaware that she did not ovulate on CD12. Oh no! She ovulated on CD13 and let’s make it late on CD13

since I have the power to do that! If Bonnie had been temping, she might have noticed that her CD12 and CD13 BBT were very low, indicating that she should keep having sex. Her BBT rose by 0.7 degrees F on CD14, a good indication that she ovulated the day before, or she is about to ovulate that very morning or day of CD14.
The moral of the story, in this particular made up situation, is that if Bonnie had been temping, she could have easily known that she still could and should have sex on CD13, even if she couldn’t on CD12. Temping would have given them a much better shot.
Example 2) Ricki and John
The pressure of trying to conceive can be insurmountable at times, not just for women. What is the one thing we need that we cannot get ourselves (more or less, lol). It isn’t like we can just get it on 5 o’clock next Wednesday and save it in the refrigerator until we need it. It is a very precious commodity and it is very time sensitive. Men catch on quick and it can really get to them. All of it can get to them. Once their performance wavers in the baby-making department, it can go to hell super quickly. I really have sympathy for the men out there trying to conceive. If I had to orgasm on command every night for a week, every month, every year, regardless of any arguments or… or…. emotions… hell, we would be childless. Think about it ladies, we aren’t talking about whether we want to orgasm every night for a week, lol, we are talking about having to get there ever single night NO matter what happens because you cannot postpone sex. For men, they have to get there every single night NO matter what.

Ricki is 42 years old and she is stressing hard over getting in enough BDs around ovulation. John’s performance has suffered a bit the last few cycles. He feels stressed about not being into sex as much and not being as turned on, yet having to perform even when he is tired as all hell. The more it happens, the more he wants to rip it off and chuck it. Ricki isn’t temping so she doesn’t have confirmation of ovulation, but she is using OPKs. They try to BD as much as John can from +OPK forward. They shoot for four days, including +OPK, but John has a lot of trouble after the first two nights. It’s getting to be a bad situation, each month is getting more intense. Truth be told, Bonnie’s feelings do get hurt and she feels undesirable, and Jack doesn’t understand why it is so hard to get turned on when he thinks his wife is sexy and “it” has never been a problem before now.

Charting her BBT showed Ricki that she always gets a temp rise two days after +OPK. Since you ovulate between 4 hours before +OPK to 28 hours after +OPK, they could have sex the night of +OPK, the next day, and the following day just to be sure and that would be absolutely sufficient. She does not have to push any harder. I didn’t even BD the day of temp rise because I was sure I ovulated days before my it occurred.
Ricki and John could even have sex only on the days of +OPK and the day after, and I would consider doing the deed on those two days good coverage. More importantly, Jack doesn’t have to feel like a big, old, useless loser with a broken ****! Maybe alternate even, sex on two days during one fertile period, and sex on three days during fertile period the next cycle. I don’t think anyone would want to admit that they aren’t having as much sex as they should be during their fertile week, but it happens. Don’t be to hard on yourself or your partner. It is very important to try to be understanding <3
Charting Your BBT Can Assist in Diagnosing Reproductive Issues
Thyroid Complications
I’ve talked with many women TTC in their forties whom have thyroid complications. I don’t wish that on my worst enemy. It’s very important to make sure your thyroid is functioning well, especially when you are TTC at a wise age 😉 Seriously though, please get your THS checked at the very least. It should be very close to 1.0 when you are TTC. Yes, your doctor might have told you 1.8 or 2.0 is okay. I don’t think that is good enough after reading about other women’s journeys TTC.
It turns out, there is an average range of BBT during the follicular phase. This range is anywhere between 97.0-97.7 degrees Fahrenheit. Having temps that fall below this range may indicate a hormonal imbalance or thyroid complications in the form of hypothyroidism. If this is something you’re noticing when tracking your BBT, it might be time for a thyroid functioning panel. (Boost Thyroid).
Endometriosis
It might be a good idea to try temping for a couple of cycles to see what information it gives you about other reproductive functioning, not just ovulation timing. Endometriosis can cause your BBT to remain elevated up to and past CD1 which is not a healthy hormonal pattern to have. A study by Chai and Wild investigated the relationship between pelvic endometriosis and altered BBT (Chai, download below).
The results of the study showed 67% of the women with endometriosis had a late decline of their BBT (after CD1). Remember, your BBT drops before your period starts. After the CL has realized there is no pregnancy to support, it stops producing hormones which signals to your uterus to release the lining and start again. If your BBT is still elevated after the first day of your period, this is a red flag that your hormones are not behaving as they should. It might be worth discussing any symptoms of endometriosis with your OBGyn.
Charting your BBT can be quite effective in letting you know you have ovulated, after the fact. It is not for predicting ovulation before it happens. Taking BBT gives you more insight into your menstrual cycle, your reproductive health and perhaps non-baby making parts as well. The most important thing to walk away with from this article knowing is that you might not be ovulating on the day you think you have been ovulating. Seriously…. it happens to the best of us. Tracking your BBT can help you narrow time of ovulation down just a little bit more 😉
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Thank you so much for being here,
<3 BK
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