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. 2024 Feb 15;26:e45139. doi: 10.2196/45139

Table 1.

Summary of the included studies.

Year Study Sample size, N Technology Measures Results
2022 Alzueta et al [7] 26 Oura Ring HRa, HRVb, and distal temperature

  • HR was higher during the midluteal phase vs menstruation (P=.001)

  • Higher HR during late luteal (P=.001) vs menses

  • Ovulation linked with lower HR vs luteal phases including midluteal (P=.02) and late luteal phases (P=.01)

  • Significant rise in body temperature during mid- and late luteal phases compared with menstruation and ovulation (P<.001)

  • Marginally lower body temperature during ovulation compared with menstruation (P=.05)
2019 Maijala et al [9] 22 Oura Ring Nocturnal finger skin temperature

  • Higher skin temperature during luteal phase vs follicular (0.30 °C, SD 0.12), and compared to oral temperature during this phase of increase (0.23 °C, SD 0.09; P<.001)

  • Sensitivity for ovulation detection using the Oura ring=83.3% (–3 to +2 days)

  • Sensitivity for menstruation detection=71.9%-86.5% (SD 2-4 days) 

  • Skin temperature correlation with oral temperature (thermometer); r=0.563 (P<.001)

  • Differentiating cycle stages; r=0.589 (P=.004)
2022 Nulty et al [10] 33 Ava bracelet Skin temperature, resting pulse rate, HRV ratio, skin perfusion, breathing rate, and movement

  • Acceptability for ovulation tracking is high, 19.3/25 (77%), with poor predictive ability

  • HRV compared with HR chest strap for direct heart monitoring + ActiGraph

  • Mean percentage error HRV=11.4%

  • Correlation against gold standard, –r=–0.28 (P<.001)
2018 Regidor et al [29] 158 OvulaRing Core body temperature

  • Accuracy is 88% for detecting ovulation (SD of 3 days around ovulation)
2017 Shilaih et al [11] 91 Wrist-worn photoplethysmography sensor HR or pulse rate

  • Rise in pulse rate during ovulatory phase relative to menstruation (median): +2.1 beats/min (P<.001)

  • Midluteal phase: pulse rate highest vs ovulation (fertile period): + 1.8 beats/min (P<.01) and relative to menses :3.8 beats/ min (P<.001)
2018 Shilaih et al [12] 136 Wrist-worn photoplethysmography sensor: Ava bracelet Body temperature (wrist skin)

  • Increased temperature on the wrist during luteal phase (+0.33 °C relative to ovulation [fertile window]); P<.001

  • Lower wrist temperature during menstruation than during luteal phases including late luteal phase (–0.38 °C; P<.001)

  • Change in temperature during the fertile period=86%
2019 Goodale et al [8] 193 Ava wrist bracelet HRV, HR, respiratory rate, and wrist skin temperature

  • Wrist temperature significantly lower during the fertile phase relative to menstruation (b=–0.25, SD 0.03; P<.001)

  • HR lower during fertile phase compared with menstruation (b=–0.03, SD 0.26; not significant)

  • HRV significantly higher during fertile stage (b=0.08, SD 0.03; P<.05) relative to the comparison of menstruation

  • Lower respiration rate during fertile period vs menses (b=–0.48, SD 0.04; P<.01)

  • HR is higher in luteal and midluteal relative to menstruation (P<.01)

  • Late luteal phase relative to menses increases in respiratory rate by 0.18 breaths per min (P<.001)

  • Accuracy for detecting fertility=90%
2019 Luo et al [25] 34 Ear device Temperature

  • Ovulation detection

  • Sensitivity =92.3%

  • Increased predictive power 23%-31.5%

  • Compared to conventional methods of fertility tracking (kit)
2021 Zhu et al [13] 63 Ava fertility bracelet Wrist skin temperature and basal body temperature

  • Wrist skin temperature decreases during menstruation (0.33 °C vs 0.04 °C for basal body temperature)

  • Sensitivity higher for the wrist temperature measure vs the standard basal body temp (oral thermometer) measure (0.62 compared to 0.23; P<.001)

  • False positive rate greater for wrist skin temperature by 5.2% compared with basal body temperature
2022 Hurst et al [24] 80 Skin worn sensor + vaginal biosensor algorithm, OvuSense, OvuCore, OvuFirst Body temperature

  • Accuracy for ovulation prediction=66% (SD 1 day)

  • 90% accuracy for the fertile window (ovulation SD 3 days)
2020 Prasannan and Sarath [26] 30 Internet of things device with a flex sensor worn on the abdomen Body temperature

  • ovulation prediction

  • Accuracy=92%
2022 Yu et al [27] 114 Huawei band + ear thermometer Body temperature and HR

  • Fertility window

  • Accuracy=87.4%

  • Menstruation cycle

  • Accuracy=89.6%
2009 Chen et al [28] 30 Abdominal sensor worn during sleep Body temperature

  • Menstrual cycle stage sensitivity=91.8%

  • PPVc=96.6%

aHR: heart rate.

bHRV: heart rate variability.

cPPV: positive predictive value.