Fall to Baseline™ Cycle Flag™ explained
Fall to Baseline is a Cycle Flag that appears when your temperature starts the cycle elevated, settles back to your normal baseline mid-cycle, then rises again at ovulation.
Noticing this pattern occasionally is normal. A pattern that keeps returning provides an insight into your hormonal health, and in particular PMOS, which is often missed in women whose periods are regular.
In this guide, we explain what the pattern looks like, what the research tells us, and when a recurring flag is worth raising with a clinician.
- Across a typical cycle, your temperature sits low and steady in the first half, climbs after ovulation, and drops back as your next period begins.
- Fall to Baseline is when your temperature starts the cycle running high, settles back to baseline mid-cycle, and rises at ovulation.
- Seeing this pattern occasionally is nothing to be concerned about.
- A pattern that repeats cycle after cycle is worth raising with a clinician, especially if you're planning a pregnancy.
What Fall to Baseline looks like
Your skin temperature isn't flat across the month. It sits at a lower, steady level through the first half of your cycle, from the start of your period up to ovulation. It then steps up after ovulation as progesterone rises, stays elevated during the luteal phase and drops back to baseline as your next period begins.
Fall to Baseline breaks the opening of that pattern. Instead of starting low, your temperature begins the cycle running high, settles back down to its normal baseline early on, and rises again at ovulation.
The Ring reads this from the overall shape of your temperature curve across the whole cycle, not from any single night.
Figure 1
Skin temperature across the cycle
Fall to Baseline: the cycle opens warm, settles to baseline, then rises again at ovulation
Skin temperature across the cycle
Ultrahuman · idealized schematic, not measured data
For the wider picture of the cycle and the hormones behind it, see the Cycle and Ovulation overview.
What the research says about Fall to Baseline
The temperature shift is measurable from the skin overnight. Across 136 women and 437 cycles, nightly skin temperature ran about 0.3°C higher after ovulation than before. That's the shift your Ring is looking out for when it traces your cycle temperature.
Unusual early patterns have been linked to PMOS. A clinical research poster using overnight temperature tracking reported that atypical temperature patterns, including an early high that falls back to baseline, were among the stronger signs of PMOS in women whose periods were regular.
PMOS (polyendocrine metabolic ovarian syndrome, the condition until recently called PCOS) is a common hormonal and metabolic condition. Regular periods often keep it from being diagnosed, which is what makes a temperature clue useful.
The authors also reported a Fall to Baseline was associated with risks in pregnancy, such as gestational diabetes and elevated blood pressure.
A large review of pregnancy outcomes found that women with PMOS had higher rates of gestational diabetes and pregnancy-related high blood pressure. Both are easier to stay ahead of when they're known about early.
How the flag appears in the app
Fall to Baseline appears under Cycle Flags on your Cycle & Ovulation page, alongside the rest of your cycle insights.
A single Fall to Baseline is unremarkable. If it keeps appearing across several cycles, that's a good reason to bring your cycle history to a clinician, especially if you're planning a pregnancy.
Read the original research
All Studies →This explainer is based on original research by the Ultrahuman Science team. Explore the full Studies repository.
Frequently asked questions
Does one Fall to Baseline flag mean I have PMOS?
No. An occasional Fall to Baseline is normal and isn't a diagnosis of anything. The pattern only becomes worth acting on if it keeps recurring, and even then it's a prompt to speak with a clinician rather than a conclusion.
Can I have PMOS if my periods are regular?
Yes, and that's part of why this flag exists. PMOS is often overlooked in women with regular cycles, and research links repeated temperature patterns like Fall to Baseline with PMOS in that group.
Why does this pattern matter before pregnancy?
Research links PMOS with a higher chance of gestational diabetes and pregnancy-related high blood pressure. Both are more manageable when known about early, so a recurring pattern is worth sharing with a clinician if you're planning to conceive.
Is a Cycle Flag a medical diagnosis?
No. Cycle Flags are wellness patterns meant to help you understand your body and, where a pattern repeats, to start an informed conversation with a healthcare provider.
References
- Shilaih M et al. Modern fertility awareness methods: wrist wearables capture the changes in temperature associated with the menstrual cycle. Bioscience Reports 2018. PMID 29175999
- Hurst B, Karoshi M. Atypical core body temperature patterns and the wider implications for conditions related to pregnancy, infertility and miscarriage risk. OvuSense clinical research poster 2020. ovusense.com
- Boomsma CM et al. A meta-analysis of pregnancy outcomes in women with polycystic ovary syndrome. Human Reproduction Update 2006. PMID 16891296
Cycle Flags describe associations in physiological data. They are not a medical diagnosis, a fertility test, or a contraceptive method. A Cycle Flag such as Fall to Baseline describes a pattern in your temperature data, not a diagnosis of PMOS or any other condition. If a flag recurs, or if you have symptoms or are planning a pregnancy, speak with a qualified clinician.
