TMI? A home hCG test that detects pregnancy and estimates weeks since conception

CalendarI'm beginning to wonder what could possibly come next. Last month, Swiss Precision Diagnostics (via its Procter & Gamble partner) unveiled its newest product in consumer diagnostics: the Clearblue Advanced Pregnancy Test with Weeks Estimator. This urine hCG test determines pregnancy status but also provides an estimate of the number of weeks since ovulation. The device has been cleared by the FDA and will be availabe in the US in September, 2013.

It works like other qualitative urine hCG tests but the body of the device contains two test strips that capture and detect the hormone in the urine sample. Detection of hCG is accomplished by the appearance of a colored band at a specific location on the test strip.

One test strip is designated "high sensitivity" and can detect a low concentration of hCG (detection limit of 10 IU/L). This test strip determines pregnancy status (pregnant or not pregnant). The other test strip has "low sensitivity" and detects higher concentrations of hCG and is used to estimate the number of weeks since conception. An optical reader housed within the device determines the color intensity of the test strips and a digital display reports the results as 1) Not pregnant; 2) Pregnant 1-2 weeks; 3) Pregnant 2-3 weeks; or 4) Pregnant 3+ weeks. The device reports an invalid result if there is a malfunction due to the device itself or operator error.

Clearblue with Estimator

Note that the weeks estimate is based on hCG concentration which is not how a pregnancy is usually dated. Physicians calculate gestational age by the day of the last menstrual period (LMP) so the device's estimate will be about 2 weeks less than one based on the LMP.

In its press release, Procter & Gamble states that the test is "more than 99 percent accurate in detecting pregnancy from the day of the expected period, and it is approximately 93 percent accurate in estimating how many weeks based on time since ovulation." I wanted to know what studies were done to support those claims but I received no response when I reached out to the individual at Procter & Gamble identified in the press release. However, there are some data included in the FDA's decision summary:

  • An early pregnancy study was conducted using 100 urine samples collected from non-pregnant women expecting to become pregnant. These samples were collected on days -6 to 1+ relative to the day of expected period. 99.0% of the devices gave a "pregnant" result by day zero (the day of the expected period).
  • A clinical study was conducted using samples from 153 volunteers with singleton pregnancies to evaluate performance of the “Weeks Estimator” feature compared to actual gestational age (method not identified). Agreement of “Weeks Estimator” with actual gestational age ranged from 45-99% (bold-faced emphasis is mine).

The bolded statement above is ambiguous but it likely is supposed to mean that the device is accurately able to estimate the true week of gestational age 45-99% of the time. If so then there are several questions that need to be answered. For example, what was the source of the range? Was it derived from different studies or from different gestational ages? What was the median gestational age? Is the device more accurate at certain gestational agess? Also, the range doesn't indicate how inaccurate the device can actually be. That is, when it is wrong how wrong is it? 1 week, 2 weeks, 3 weeks, or even more?

Given that the "Weeks Estimator" is highly variable, it is likely that Procter & Gamble will include language (similar to what the FDA stated) to caution the consumer that "the 'Weeks Estimator' is meant solely as an estimate for the consumer and is not intended as a substitute for a doctor’s clinical diagnosis. The ‘Weeks Estimator’ is not intended for multiple pregnancies. The estimate provided by the device may be inaccurate in these cases."

From a practical perspective, while women may want/need to know when they conceived, this is not the device to accomplish the job. It seems to provide highly variable information that, at best, is just a curiosity. Procter & Gamble says “confirming pregnancy is a life-changing moment in any woman’s life, and it sparks so many immediate questions like 'when did I get pregnant?'" True, but necessary? I'm not convinced.

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