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I went off hormonal birth control about 3 months ago and switched to the Fertility Awareness method of birth control. One thing I need to do for this method is chart my basal body temperature every morning. To do this, I needed a basal body thermometer (a very accurate thermometer). I bought the Baby Mad Basal Thermometer off Amazon for £4.99 because there were a fair number of decent reviews and I couldn't find a better option. Sadly, I'm afraid even though this is cheap it isn't worth the money I paid.
For fertility charting you need a thermometer accurate to at least 0.1°F or 0.05°C because the thermal shift which indicates ovulation is very small in most women. A normal fever thermometer is usually not precise enough. The Baby Mad Basal Thermometer gives readings to 1/100th of a degree Celsius (2 decimal places) with a claimed margin of error of just + /- 0.05°C. It has an easy to read display, is mercury free, is supposed to beep when the final temperature is reached, and has a memory recall feature.
My first issue with this thermometer arose when I left it in a little longer than usual. I hadn't turned on a light (trying not to wake my husband on a Saturday morning). I suppose it turned itself off automatically after about 3 minutes (not the 10 minutes it claims in the instructions) because when I hit the button to turn off the thermometer I actually turned it back on- thus loosing my saved temp. Later that morning I discovered my mistake and retook my temp- but it gave me a reading far to high because I hadn't had the required 3 hours sleep and it was later than my usual temping time. However, it spit out the EXACT same oddly high temp the following two mornings (despite being at my normal time after a full night's sleep). It was my first month off hormonal birth control, so I expected some unconventional temperature shifts, but this was suspicious. The second morning I retook my temp right away and it gave me a temp .14C LOWER than the first reading (you would expect temps to rise as your body starts to wake up). A few days later it again switched off after less than 5 minutes (thankfully this time I had the light on and realized before losing my temp).
Next, this thermometer beeps too quickly. The instructions say it beeps after you temperature stabilizes which it defines as changing less than .1C in 16 seconds, but I found my thermometer beeping between 16-20 seconds after inserting it- meaning it claims it has not changed more than .1C from the first 0-4 seconds of reading (which is simply not the case- I can watch the numbers to know they are changing). So the beep is useless. In addition, for accurate charting, you need to have temps to the nearest .05C so that definition of a stable temperature just isn't good enough. Oddly, after using the thermometer for about a month it started beeping later (perhaps 30-40 seconds after insertion). Then after a few weeks of that it started beeping after just 10 seconds. I'm not sure what caused the change, but the inconsistency is worrying . Instead of relying on the beep, I usually leave the thermometer in a full minute. Sometimes the temp at the beep is as much as .35C off that temp at the minute mark (keep in mind a temp shift of just 0.1C is enough to indicate ovulation... so these differences are more than enough to make fertility charting impossible).
Additionally, after just a month of use, the memory function became unreliable. Several times I lost my temperature because the memory function failed to work (I often wake up before the alarm and need to take my temperature without waking my husband so don't turn on the light).
Finally, I have serious doubts on the accuracy of this thermometer. One day I had it give me a basal temp of 36.82- that afternoon I took my temp again out of curiosity and it gave me a temp of 36.84 (so it was claiming my basal temp was just .02C less than my normal temp- unlikely). On another day, it claimed my basal temperature was actually half a degree higher than a temperature I took after moving around for half an hour.
I tried replacing the battery, but my problems with this thermometer persisted. This thermometer might be suitable for a fever thermometer if you aren't too concerned about true accuracy, but it is fairly useless as a basal/fertility thermometer. Sadly, there don't seem to be any good options. Boots no longer makes theirs (which was reported to be very good) and BD has been bought out by 3M/Nexcare and there have been a lot of complaints about a reduction in quality since then. (What I would give for a glass mercury thermometer...).
Update 21 Oct 12: Shortly after writing this review I bought the Nexcare Basal thermometer mentioned above. I have been very happy with it and would recommend giving it a try if you are in need of a decent basal thermometer (I'll write a full review soon).
All that said, this thermometer does have some good points. The display is clear and easy to read, it is easy to turn on and off and the beep is quiet enough for me to hear without waking up my husband (shame I can't rely on the beep). Also, it has a nice thin shape which makes it perfect for vaginal temping (vaginal temping is more accurate than oral and is much better for mouth breathers like myself). Plus the streamline shape makes it very, very easy to clean, but these mean nothing if it doesn't give a decent temperature reading.
I was tempted to give this thermometer 2 stars, since the other options don't seem very good either, but just this morning the thermometer glitched again (I'm about to ovulate- so it is the most important time of the month to have accurate readings). That means out of the 3 cycles I have used it, this thermometer has had problems 2 of those months during the most critical time- frustrating to say the least. So it is just getting one star from me.