Quality of Fertility Monitors Assessed by German Researchers
Fertility Monitors

Richard J. Fehring
Reprint from Current Medical Research
Vol 15, No 1-2, Winter/Spring 2004
Washington, DC
Reproduced with Permission

Over the past ten to fifteen years a number of fertility monitors have been developed to help women users determine the fertile phase of their menstrual cycles. These monitors include several varieties of miniature microscopes designed to visualize dried saliva and salivary ferning patterns that indicate fertility (i.e., PG 53, Maybe Baby, PC 2000), three computerized basal body temperature (RET) monitors that include built in temperature and calendar algorithms (i.e., the Bioself, Cyclotest 2 Plus, Babycomp / Ladycomp) and a hormonal monitor that measures urinary metabolites of E3G and LH (i.e., the Persona). German researchers from Dusseldorf and Heidelberg recently evaluated these monitors in comparison with the Symto-Thermal method (STM) of Natural Family Planning in order to make recommendations on their quality and effectiveness in helping women and couples avoid pregnancy.1

Each of the three types of salivary ferning monitors (listed above) was paired with one of the computerized BBT monitors and evaluated by 5 women volunteers. This resulted in each of the monitors being utilized by 15 women. Another 15 women who used the STM to determine their ferdle phase were paired with the Persona hormonal fertility monitor. The women participants were between the ages of 21 and 42 with previous cycle lengths between 17 and 40 days. The first 6 cycles of use of each of the computerized BBT monitors and the personal hormonal monitor and 3 cycles of use of the salivary ferning monitors were considered "learning cydes"and the next cycle (i.e., the 7th or 4th) was considered the "test cycle." During the test cycle the women participants underwent daily pelvic ultrasound scanning of their ovaries and the dominant follicle and utilized a Clearplan urinary test kit to determine their surge in LH. The estimated day of ovulation (EDO) was considered to be 12 hours past the maximum follicular diameter and 24 hours past the urinary LH surge. The researchers recruited 65 women volunteers, of which 62 (mean age 31) contributed 122 test cycles.

The fertile phase as determined by each of the monitors and the STM was compared with an 8-day theoretical fertile phase based on the EDO. The eight-day theoretical fertile phase included the EDO, and the 5 days before and the 2 days after the EDO. The researchers also evaluated the monitors and the STM on the day specific probabilities of pregnancy during the 8-day theoretical phase of fertility. The day specific probabilities were taken from a previous study that utilized the BBT shift as the reference point. From this data the German researchers were able to calculate the correct identification of the days of fertility, and the false negative and false positive days for each monitor and the STM. They then gave an overall quality score for each of the monitors and the STM. The quality scores were between O and 1, with the smaller the score (i.e., the score closest to 0) indicating a good method for preventing pregnancy. A score near 1 would indicate that the method was not much better than using no method.

The salivary fertility monitors had the highest false negative rates (i.e., a theoretically fertile day that was indicated as infertile by the monitor) from 51.6% to 73.4% of the cycle days monitored, followed by the Persona hormonal monitor (20.8%) and then the computerized BBT monitors (1.7% to 4.7%). The STM had "O" false negatives. The highest false positive readings (i.e., a theoretically infertile day which was predicted as fertile by the monitor) ranged from a low (6.6%) by the PG 53 salivary ferning monitor and a high (53.9%) with the computerized Bioself BBT monitor. The Persona fertility monitor had a 23% false positive rate and the STM a 25.3% false positive rate. The STM had the highest correct rate of predicting the fertile days (82%) and the Bioself BBT monitor had the lowest (58.4%). The Persona had a 77.6% correct fertility rate.

The German researchers calculated that the STM obtained the best quality score (0.000) and lowest average day specific probability of pregnancy (0.000). The computerized BBT monitors obtained the next best quality scores (range 0.0483 to 0.1213) and lowest average day specific probability of pregnancy (range 0.0134 to 0.0336). The Persona hormonal monitor had a quality score of 0.4169 and an average day specific probability of pregnancy of 0.1155. The salivary ferning microscopes received the lowest quality scores (range 0.8349 to 0.8552) and the highest day specific probability of pregnancy (range 0.2313 to 0.2369).

The German researchers conduded that only those monitors that received quality index scores of less than 5 should warrant further study and be utilized in large prospective populationbased effectiveness studies. Based on their findings they only recommended that the STM, the computerized BBT monitors and the Persona monitor be further studied in large prospective clinical trials. The salivary ferning monitors were not recommended for client use or for population based efficacy studies.


There is a need to evaluate fertility monitors that can be purchased by the consumer and are readily available. The German researchers from the University of Dusseldorf and Heidelberg conducted an objective study of fertility monitors that are available in Europe. The study utilized gold standards (i.e., follicular ultrasound and urinary LH) to estimate the day of ovulation and to evaluate the fertile phases as determined by 7 fertility monitors and the STM. For the most part I agree with their methodology and results, however, I have some observations and concerns.

First of all, I found it interesting that they utilized an 8-day window of fertility rather than a 6-day window that has become somewhat standard in fertility assessment. The 6-day window is based on several research studies at the National Institute of Environmental Health Sciences and that have been reviewed in the CMR.2,3 With an 8-day window you will find less false positive days on fertility monitors that are less precise, i.e., like the BBT monitors and the STM, and more false negatives with more accurate devices like the Persona. For example, if you would base the accuracy of a given fertility monitor on a 6 day window of fertility - with day 6 the EDO, then, a monitor that indicated "fertility" on EDO minus 6 or 7 days or EDO plus one day would be considered a false positive, but with the 8-day window they would not. The results of this study were also biased towards the STM and electronic BBT monitors since the estimated day specific probability of pregnancy are based on a BBT shift model -- a model that utilized a less precise indicator of fertility and the EDO.

It is not astonishing that the STM had zero false negatives, since the average estimated days of fertility are double the 6-day window of fertility. However, that it only had a 25% false positive rate is. When almost double the actual days of fertility are common with the STM method, one would expect a dose to 50% false positive rate.

I also found it rather fascinating that one of the markers of the EDO was the urinary LH surge detected with the Clearplan fertility test kit. The Clearplan LH test kit and the Persona monitor are made by the same company (i.e.,Unipath). The Persona monitor uses a similar assay of urinary LH to determine the beginning of the end of fertility. Although Persona has an estimated correct use failure rate of 6.4%, the Persona with a new algorithm needs to be prospectively tested in a population of users to determine its actual population effectiveness. A recent Italian study at the University of Naples evaluated the accuracy of the Persona monitor.4 The Italian researchers utilized 20 volunteer women participants who generated 200 cycles of data. The women participants were also monitored with follicular ultrasound and serum LH to estimate the theoretical fertile window and the EDO. The Persona monitor provides the user with a green light to indicate infertility and a red light to indicate fertility. The beginning of the fertile window by ultrasound was in agreement with the beginning of fertility by the Persona (i.e., the first Red day) 94% of the time, the ultrasound EDO agreed with the Persona EDO 95.8% of the time, and the ultrasound first day of infertility (after ovulation) agreed with the Persona first green day after the red fertile days 97.5% of the time. The Italian researchers conduded that the Persona was effective in recognition of the fertile phase and stated that it was a welcome alternative for couples that want to use NFP. (Richard J. Fehring)


1 Freundl, G., Godehardt, E., Kern, P.A., Frank-Hermann P., Koubenec H.J. and Gnoth, Ch. Estimated maximum failure rates of cycle monitors using daily conception probabilities in the menstrual cycle. Human Reproduction. 2003:18(2):2628-2633. [Back]

2 Wilcox A.J., Weinberg C.R. and Baird, D.D. Timing of sexual intercourse in relation to ovulation, effects of the probabiliq of conception, survival of the pregnancy, and sex of the baby. New England Journal of Medicine. 1995;333:1517-21. [Back]

3 Dunson, DB., Baird, D.D., Wilson, A.J. and Weinberg, C. Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation. Human Reproduction. 1999;14:183549. [Back]

4 Guida, M., Brarnante, S., Acunzo, G., et al. Diagnosis of fertility with a personal hormonal evaluation test. Minerva Ginecol, 2003:55(2):167-73. [Back]