The Best Pregnancy Tests

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(CBS) "Is it possible that I'm pregnant?" can be one of the most nerve-wracking questions for a woman to deal with. But with so many pregnancy tests on the market today, how can you tell which is relaiable?

Consumer Reports senior editor Nancy Metcalf talks about the best pregnancy tests available. Get the recommendations on Tuesday’s The Early Show.

Method:
All home pregnancy test kits use monoclonal antibodies to detect a hormone known as human chorionic gonadotropin (hCG), which is produced by the developing placenta beginning on the day on which the embryo implants in the uterine wall. Concentrations of this pregnancy hormone vary widely from woman to woman, but the more sensitive tests can measure lower levels of hCG.

All 18 brands tested by "Consumer Reports" (CR) employ similar technology - most use sticks with absorbent wicks that are held directly in the urine stream, and most allow women to collect urine in a cup and then dip the stick. Regardless of collection method, reading the results is the same for every kit: if a line appears in the window after a specified number of minutes, the test is positive.

Working with an independent laboratory that specializes in hCG studies, CR spiked hCG-free urine with varying concentrations of the hormone "to mimic the range found in normal early pregnancies."

They tested each product at increasing levels of hCG concentration until a positive result was attained.

"We conducted the tests as instructed on each product's package insert," CR says. "Technicians read the results after the specified minimum wait - anywhere from 1 to 5 minutes, depending on the product - and then again at the maximum time allowed (10 minutes in all the products we tested)." Kits were rated on efficacy, ease of use, and ease of result readings.

Performance:
One kit, the First Response Early Result Pregnancy Test, emerged as the most reliable and sensitive test. "It detected hCG at concentrations as low as 6.5 mIU/ml (thousandths of an International Unit per milliliter) - that's almost sensitive enough to detect any pregnancy soon after implantation," CR wrote. "Most other kits were far less sensitive - the five least sensitive tests couldn't detect hCG below concentrations of about 100 MIU/ml at their specified reading times. However, when we waited a full 10 minutes before reading the results, seven of the test kits performed much better than they did at the manufacturer's suggested waiting time."

Although all the kits were "easy to use," First Response and two other tests (Answer Quick & Simple and ClearBlue Easy) produced result lines that were more intense than others at lower concentrations of hCG, making them easiest to read.

In the end, First Response's Early Result Pregnancy test ($18.09/2 tests) came out on top, with an "Excellent" rating (winning an "excellent" score in hCG sensitivity, "good" in ease of reading, and "excellent" in 10-minute hCG sensitivity, with an overall recommendation of "best combination of sensitivity and reliability). Confirm's Pregnancy Test ($11.19/2 tests) scored lowest, with a final score of "Poor" ("fair," hCG sensitivity; "poor," ease of reading; and "fair," 10-minute hCG sensitivity, with some samples failing to work properly).

Ratings

First Response Early Result Pregnancy Test
($18.09 for two)
Consumer Reports Rating: Excellent

Confirm Pregnancy Test
($11.19 for two)
Consumer Reports Rating: Poor

Recommendations:
Although CR calls the First Response test "a superior choice," it warns, "Women need to use home pregnancy test kits with a clear understanding of their limitations."

It explains that testing for hCG is not the same in all women. In 10 percent of pregnant women, the embryo does not implant until after the first day of a missed period (and again, hCG is not produced until the embryo implants in the uterine wall).

"Until implantation, it doesn't matter how sensitive the test is," CR says, "You can't detect the pregnancy before it's producing the stuff that you're measuring, which is hCG."

Even pregnancies that have implanted may produce too little hCG for many at-home tests to detect, especially only a day or two after a missed period and when read after the manufacturer suggested waiting period specified in test packaging.

"Some kits improve in detection when read after a wait of 10 minutes, but waiting longer than that may produce a negative result that looks faintly, misleadingly positive," CR reports.

Moreover, about one-third to one-quarter of pregnancies implant for a short time, then fail. "That leads to a transient rise in hCG, which can extend for as long as two days after the day of the missed menstrual period."

Consumer Reports advises, "If you're comfortable waiting, a sensitive test taken a week after your period is overdue will almost certainly give you accurate results. If you elect to take the test as early as the day after you've missed your period, remember that a negative result isn't 100 percent certain. And a positive result may mean either a viable pregnancy or a pregnancy destined to end shortly after it began. With either of those results, you should plan on testing again a week later, just to be sure."

Source: http://www.cbsnews.com/stories/2003/01/27/earlyshow/health/main538075.shtml

Category: HCG, implantation, pregnancy