I've just answered a question in another thread which has drawn my attention to the fact that the Clearblue Fertility Monitor may not be suitable for everyone. I thought it would be a good idea to post the following as it could prove useful for those thinking about purchasing one. If nothing else, it will help people decide whether it would be useful for them, before they spend their money. It's a direct quote from the booklet that comes with the monitor.
Limitations on Use
"The Clearblue Fertility Monitor is suitable for women whose natural cycle normally lasts between 21 and 42 days. The majority of women will need 10 Test Sticks in each cycle. However, women with irregular or long cycles may have to use 20 Test Sticks each cycle in order to detect their most fertile time.
Certain medical conditions and medications can adversely affect the performance of the Monitor. Women who have menopausal symptoms, polycycstic ovarian syndrome, impaired liver or kidney function, are pregnant or have recently been pregnant (even if not carried to full term), may get misleading results. Similarly misleading results may be obtained by women using antibiotics containing tetracyclines, hormonal treatments (eg hormonal contraception, hormone replacement therapy), fertility treatments containing human Chorionic Gonadotrophin (hCG) or Luteinising Hormone (LH), or any treatment that might affect their cycle. Clomiphene citrate may elevate estrogen levels and this may result in High Fertility being declared early in the cycle and more High Days being displayed, and in some cases the Monitor may not show Peak Fertility even when ovulation occurs. We therefore recommend that women taking clomiphene citrate consult their doctor for advice before using the Clearblue Fertility Monitor. Always read the manufacturers instructions for any medication that you are taking before conducting a test.
Women who have recently been breastfeeding, using hormonal treatments (eg hormonal contraception, including emergency contraception, fertility treatments, hormone replacement therapy), or any other treatment that might affect their cycle, may wish to wait until they have at least two natural menstrual cycles in a row (each lasting 21-42 days), before using the Clearblue Fertility Monitor.
Women who have recently been pregnant (even if not carried to full term) may still have hCG in their bodies. HCG can adversely affect the performance of the Monitor. Therefore they are advised to wait until they have had at least two natural menstrual cycles in a row (each lasting 21-42 days), before using the Clearblue Fertility Monitor.
Please speak to your doctor if you need further advice."