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Avoiding pregnancy

Achieving pregnancy

Instructions for use
of the Hormone
Fertility Monitor

Instructions for use
of cervical mucus

Instructions for combining
signs of fertility


Caution on
testing urine
You should be aware that the ClearBlue monitor misses the LH surge in about 1 out of 10 cycles. When that happens, the monitor will continue to ask for test strips for 20 days and you will have 20 days of high fertility readings. That is why there is a formula for the end of the fertile phase (i.e., the latest Peak day of the last 6 cycles plus 3 full days) when that happens. If you experience a missed LH surge (Peak day) more often then 1 out of 10 cycles, you might be testing your urine the wrong way, e.g., holding the test strip too long under the urine stream. If that happens, you might collect the urine in a small container and dip the test strip in the urine for a timed 15 seconds.
Instructions for Achieving
or Avoiding Pregnancy

(Hormone Fertility Monitor)

The Marquette Model of NFP was developed for use with the ClearBlue fertility monitor along with a simple algorithm to avoid or achieve a pregnancy. The instructions assume that the user has purchased a monitor and has read the user manual for proper use and care. The following instructions start on the first day of the user’s next menstrual cycle. The menstrual cycle begins on the first day of menses, i.e., the first day of the period.

example cycle using the ClearBlue monitor
Charted Cycle Example: ClearBlue Fertility Monitor

There are only 6 days of fertility during a menstrual cycle - the day of ovulation and the 5 days before. The 6 days are called the "fertile window."  You need to know the beginning, peak and end of the fertile window. The monitor determines the fertile window by measuring urinary metabolites of two female reproductive hormones, estrogen and LH. The monitor will indicate three levels of fertility – low, high, and peak. The monitor does not always provide an early enough warning of the beginning of the fertile phase, and it will miss a peak fertility reading in about 8% of cycles. Therefore, simple instructions have been developed to go along with the monitor. 

Do not have intercourse, genital contact, or practice withdrawal during the fertile window – i.e., from the first day of fertility through the last day of fertility. The length and time of the fertile window will vary from cycle to cycle. Couples who are using the ClearBlue fertility monitor as an aid to avoiding pregnancy will be asked to refrain from intercourse on all "high" and "peak" days and to use the following instructions for determining the fertile window.


Fertility BEGINS on day 6 of the first 6 cycles.
  After 6 cycles,
Fertility BEGINS on the earliest day of "peak" during the last 6 cycles minus 6 days or the first "high" reading on the monitor - whichever comes first.


Fertility ENDS on the evening of the 4th day following the last "peak" day on the monitor.
  After 6 cycles,
Fertility ENDS on the evening of the last "peak" day of the last 6 cycles plus 3 days, or the last "peak" day on the monitor plus a count of 3 full days - whichever comes first. 

These instructions are to be used only for those women who have cycles between 22 and 42 days in length and who are between the ages of 20-42. If there are two or more cycles that fall out of that range or the menstrual cycles vary by more than 10 days, see your professional NFP teacher for advice. After the first 6 cycles the fertile window is re-calculated (based on the previous 6 cycles) for each cycle.

Those women who are coming off hormonal contraception, who recently were pregnant, or who recently stopped breastfeeding should wait until they have at least 2 natural menstrual cycles in a row before using the monitor and following these instructions.  There is a separate protocol for women who are breastfeeding and not in cycles. Women who have polycystic ovaries need to have their cycles regulated before using this protocol. The monitor will not be accurate for women who are on fertility drugs. Tetracycline antibiotics may also affect accuracy of the monitor.   

Have intercourse on the High and Peak days of the monitor.

There is a separate protocol for women who are breastfeeding and not in cycles.

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