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Developing a fertility monitor

Posted: 11 Mar 2013 ?? ?Print Version ?Bookmark and Share

Keywords:health monitoring systems? fertility monitor? basal body temperature?

The field of electronics plays a crucial role in designing clinical equipment ranging from a small digital thermometer to complex health monitoring systems. Even critical implantable devices (such as cochlear implants, cardiac pacemakers) rely on electronics for signal conditioning. This article focuses on the design of a fertility monitor.

Need for a fertility monitor
A fertility monitor is a small portable device used to monitor the fertility levels of a woman by checking the hormone levels in her body. Because a woman doesn't have the same level of fertility every day, when a woman wants to get pregnant, she tends to look for a day when the fertility level in her body is at the highest. A fertility monitor test hormone levels to identify when levels are the highest.

Typically, a woman's menstrual cycle has a duration of 28 days. This overall menstrual cycle has three phases where the peak fertility occurs during a period between the second and the third phases. This period of peak fertility is also known as the ovulation period. Certain hormonal changes during the ovulation period can result in measurable changes like an increase in luteinizing hormone (LH) in urine and an increase in basal body temperature (BBT) (usually one or two days before ovulation).

Figure 1 and figure 2 show how the LH- hormone concentration and the basal body temperature (BBT) are distributed throughout the 28-day cycle period.

Figure 1: LH concentration vs. days.

Figure 2: BBT vs. days.

Working of some of the common fertility sensing techniques
Let us review the two basic fertility sensing techniques (LH concentration measurement and BBT measurement) before going to the overall system design.

A. Urine based LH concentration measurement:
Here a test strip is used which has three marked levels:

???Stop line
???Test band
???Reference band
Initially, only the stop line marking is present in the strip.

A small amount of the women's urine is taken in a cup. The test strip is dipped into the cup in such a way that the urine level does not exceed the stop line marking (figure 3).

Figure 3: LH testing procedure.

This strip is removed after few seconds and kept flat for a few minutes, after which appear the test band and the reference band. The reference band used for comparison, and if the test band is darker than the reference band, this indicates a higher LH hormone concentration. In other words, it indicates that the woman is about to reach her ovulation period. If it is lighter, this means she has not reached the ovulation period yet.

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