Menstrual Cycle and HRV: Why Your Baseline Moves

Does HRV change across the menstrual cycle?

Heart rate variability (HRV) is the beat-to-beat variation in the interval between heartbeats. It shifts from night to night for many reasons, and the menstrual cycle is one of them (why HRV changes from day to day).

On average, the shift is small. A living systematic review of 16 studies looked at HRV from wearables and phones [S1]. In naturally menstruating women, HRV was higher at the beginning of the cycle and lower toward the end, with differences in time-domain HRV of 3 to 9% [S1]. The studies defined cycle phases differently, so the authors could not pool them into one estimate [S1]. An earlier meta-analysis of laboratory studies pointed the same way: vagally mediated HRV was lower in the luteal phase, the second half of the cycle after ovulation, than in the follicular phase, the first half [S7].

A study that followed 193 women over 293 menstrual cycles with a consumer fitness tracker saw the same shape in daily data: SDNN, RMSSD and high-frequency power fell before a period and rose after it [S2]. This happened both in women with and in women without premenstrual disorders [S2]. Only in the women with premenstrual disorders did lower HRV go together with stronger symptoms [S2]. This is a single cohort that used one tracker brand.

One timing detail comes from a laboratory study of 33 women who attended eight clinic visits across the cycle, with ovulation timed by the LH surge in blood [S4]. High-frequency HRV dropped around ovulation [S4]. This is a single small study, and it is probably one of the studies inside the review above, so it is not an independent confirmation.

Does every woman follow the same curve?

A common picture is that every woman's HRV follows the same textbook curve: higher in the first half of the cycle, lower in the second. A recent study tested this with daily measurements in 21 naturally cycling women [S6]. The researchers aligned each cycle precisely to its ovulation, so that cycles of different lengths could be compared [S6]. On this scale the population-level rhythm of RMSSD was flat and not significant, while each woman's own cyclic pattern was significant [S6]. In other words, there was no single shared rhythm, and individual patterns differed [S6]. Poorer sleep, higher stress and greater fatigue on a given day went with lower HRV in that woman [S6]. This is a single small study using a smartphone camera, but its result runs against the idea of one curve for everyone.

The average from many women and the pattern of one woman are different things. The average can show a small fall toward the end of the cycle while your own cycle shows a larger fall, a smaller one or none (interpreting HRV).

What else moves the numbers?

The largest dataset comes from wearable users. A retrospective study analysed 1.2 million days of data from 2,596 women who logged 42,759 menstrual cycles; the women wore a WHOOP band [S3]. Cycle length was strongly associated with how much heart rate, HRV and breathing rate varied across the cycle [S3]. Variation across the cycle was greater in people who slept less [S3]. Within the same people, less sleep raised resting heart rate regardless of the cycle phase: resting heart rate rose by 1.2% with a 10% decrease in weekly sleep [S3]. Three of the authors were WHOOP employees who hold company shares [S3].

Daily behaviour can therefore matter as much as the phase itself. Sleep shapes night-time HRV in any phase (HRV and heart rate during sleep).

What about hormonal contraception?

In the living systematic review, users of hormonal contraception had lower HRV than naturally menstruating women, particularly in the late cycle [S1]. This comes from observational studies of different products and regimens. This page does not compare contraceptive methods and gives no advice on choosing one; that is a conversation with a doctor.

What about menopause?

In the same review, HRV tended to decline after menopause with increasing age [S1]. A small laboratory study of 41 healthy women (13 after menopause and 28 before) looked closer [S5]. Women after menopause had lower resting HRV, but the difference was no longer significant after adjusting for age and body mass index [S5]. What differed was the response to a drug that raises blood pressure (angiotensin II): high-frequency HRV fell in the women after menopause [S5]. In the women before menopause, resting HRV did not differ between the two cycle phases studied [S5]. This is a single small study with a laboratory drug challenge, not everyday stress, and it does not support any conclusion about treatment.

What does the evidence show?

What we don't know. Predicting the cycle phase or ovulation of one woman from her HRV has not been shown in the studies on this page. The average shift across the cycle is small compared with the night-to-night noise of wearable HRV, and individual patterns differ [S1] [S6].

By evidence class.

• Context-dependent. On average, wearable HRV is higher early in the cycle and lower toward the end, and the difference is small [S1] [S7]. Hormonal contraception is associated with lower HRV, especially late in the cycle [S1]. In real-world data, cycle length and sleep affect how much the numbers move [S3].
• Emerging. A dip before a period occurs in women with and without premenstrual disorders [S2]; high-frequency HRV dropped around ovulation in one laboratory study [S4]; after alignment to ovulation the shared rhythm was flat and individual patterns dominated [S6]; lower resting HRV after menopause was largely explained by age and body mass index [S5].
• Unknown. Whether HRV can tell one woman which phase she is in or when she ovulates.

What it does not tell you

• HRV is not a fertility or contraception tool. Nothing here shows that HRV can tell when you are fertile, and it must not be used for contraception.
• It does not diagnose anything. A dip before your period is part of the average pattern, not a sign of a premenstrual disorder or any other condition [S2]. Painful, very irregular or heavy periods, or symptoms that disrupt daily life, need a doctor, whatever a wearable shows.
• It gives no advice on contraception or menopause treatment.
• Population data are not a prediction for you. The averages come from many women; your own cycle may show a larger shift, a smaller one or none [S6].
• Company data carry a caveat. The largest dataset was co-written by employees of the device maker [S3].
• One study inside a review is not two confirmations. The ovulation study is probably part of the review's evidence base [S1] [S4].

In ONDA

ONDA builds a personal baseline from nightly values stored in Apple Health — from Apple Watch or another device that syncs heart data there [S8]. The window is 14 days, and ONDA compares each night with your own corridor — the average of your recent nights plus or minus one standard deviation — and flags a night only when it is at least 1.5 standard deviations outside and has changed by a minimum amount. Apple Health records HRV as SDNN, so ONDA's HRV trend is an SDNN trend. ONDA does not track the menstrual cycle, so the baseline does not adjust for cycle day. A lower HRV in the days before a period may be an ordinary cycle fluctuation rather than a warning. If you want to see your own pattern, note the cycle day yourself and compare the same days across several cycles, rather than comparing yourself with phase averages from other women (your HRV baseline; how HRV is measured). ONDA does not determine fertility, ovulation or contraception from HRV, and it does not diagnose any condition.