Pregnancy Tests

How pregnancy tests work

Pregnancy tests detect the presence of a hormone called human chorionic gonadotropin, or hCG, which is produced by the developing placenta soon after an embryo attaches itself to the uterine lining. The amount of hCG present in a woman's body increases rapidly in the subsequent days. Home pregnancy tests are based on the presence of hCG solely in the urine, though your physician may also use a blood test. HCG is measured in thousandths of International Units, or mIU. The most sensitive tests can detect hCG levels as low as 15 to 25 mIU. This level is present in the urine of most pregnant women about eight to eleven days after ovulation or about the first day after a missed period. With less-sensitive tests, you have to wait longer for an accurate result.

To make any test easier to interpret, experts say it's best to use first-morning urine, because it's the most concentrated. If this isn't possible, avoiding urination for several hours before testing can also be helpful. You should check for results when the instructions say to do so. For example, if you leave the test to sit for too long, an evaporation line may develop and look enough like a positive result to cause confusion.

Almost every brand of pregnancy test receives some negative consumer reviews at Epinions.com, because the test was negative on the first day of a missed period, then the woman tested positive a few days to a week later. Contributors who experienced this say that the test failed to work. However, medical experts point out that in as many as 10% of pregnant women, the embryo doesn't implant until after the first day of a missed period. Until implantation occurs, and the placenta begins developing, there is no hCG in the body to be detected by a pregnancy test.

There are several other variables influencing the accuracy of a pregnancy test, including how well the instructions for use were followed. Another factor may be hCG already present in the body from a miscarriage, recent birth, or some fertility drugs. Testing after drinking a large quantity of liquid may also result in a false negative, due to diluted urine. Detergent or soap residue can contaminate a collection cup. Exposing the test strip to heat, sunlight, or vibration may affect results. Finally, excess protein or blood in the urine, as well as other medications like Thorazine, Dolophine or Methadose can influence results.

Digital pregnancy tests

Standard pregnancy tests display results as lines of dye, indicating the presence of hCG. All tests have a control line to indicate the test is working properly. Most use a second line, either in a separate window or in a plus-sign shape, to indicate a positive result. But according to reviews and to those who've used pregnancy tests, deciding whether or not you see that second line can be open to some interpretation, and if you wait more than 10 minutes to read the result, a urine evaporation line could look an awful lot like a positive pregnancy indicator line.

The Clearblue Easy Digital Pregnancy Test (*est. $20 for two-test kit) attempts to make reading between the lines easier, letting women know their results with words instead of hard to interpret lines. The test does the interpretation for you, displaying the words "pregnant" or "not pregnant" in a little window. Practically speaking, the Clearblue digital pregnancy test works like any other test -- you place the absorbent strip under your urine stream for 5 to 7 seconds. A flashing ‘test ready’ display appears for 20 to 30 seconds to let you know the test is working properly. Within 3 minutes, the results are spelled out with either a ‘pregnant’ or ‘not pregnant’ reading. The test results remain on display in the window for up to 1 hour – at which time the device shuts off.

Although digital pregnancy tests are supposed to reduce confusion about results, we still found plenty of complaints about the Clearblue Easy Digital test. With standard pregnancy tests, two lines indicate a positive test (one line is the control line, and one line indicates the presence of hCG). However, with the Clearblue digital test, the appearance of two lines has no bearing on the result. This results in lot of confusion for women who have experience with other tests and are disturbed that the result reads "not pregnant," yet there are two dye lines on the test strip. According to the manufacturer, these lines appear because the test also measures another hormone (which has no bearing on pregnancy) present in urine.

We also found some other complaints about the Clearblue digital pregnancy tests. Some women get a "test malfunction" reading, and we read reports of incorrect assembly or a dead battery – in which cases the test cannot be used. Altogether, reviews say there's little advantage to digital pregnancy tests, and interpreting their results can be almost as frustrating as with regular tests. Digital tests are also more expensive than regular tests.

The e.p.t Certainty Digital Home Pregnancy Test (*est. $20) is the other digital test available on the market. The makers of Clearblue won a patent infringement lawsuit against the makers of e.p.t Certainty (Pfizer) because the products are so similar. There is potential for errors with e.p.t as well, in which case a 'see leaflet' message appears indicating something is wrong and requiring the tester to wait 30 minutes before trying again. As with Clearblue, some of the e.p.t tests are sold with 2 test strips. The holder portion of the kit can be reused with a new test stick, but it is important to note that the holder should be clear of any urine that may be left from previous testing.

Best pregnancy tests

First Response Early Result (*est. $15 for two-strip kit) is ranked first by two of the best review sources we found. It consistently detected 12.5 mIU of hCG in independent testing, making it the most likely test on the market to detect pregnancy on the first day of a missed period (95% of the time in product testing). First Result is claimed by the manufacturer to detect 15 to 25 mIU of hCG, but both sources say that First Response even detected hCG levels as low as 6.3 and 6.5, soon after implantation -- even before a missed period. First Response is available in one-, two , and three-strip kits ( *est. $15 and $18 , respectively).

We found a few consumers posting at Epinions.com who say that First Response Early Result didn't work because they tested negative before or at the time of their missed period, then tested positive a few days later. Keep in mind that in 10% of pregnant women, implantation hasn't occurred yet at the time of a missed period (so no pregnancy test will be positive). We found just as many complaints about First Response Early Result as we did for all other tests.

Because of this, experts say it's a good idea to get a kit with two testing strips and to wait a week between each test. Clearblue Easy Earliest Results (*est. $14) has two strips for slightly less expense than First Response above and detects 25 mIU of hCG. In product testing, Clearblue comes in second to First Response, detecting pregnancy on the first day of a missed period 80% of the time. Even though Clearblue is a little cheaper than First Response Early Result, most women will prefer to pay extra for an earlier result with First Response.

Experts say that women who are prone to false positives because they have hCG in their systems from a recent birth or miscarriage, or because of certain fertility drugs, may be better off with a less sensitive test. That way, the test will only pick up an increase in hCG associated with a pregnancy, not the low "background" level. Fact Plus (*est. $12.50) detects 100 mIU of hCG. One- and two-strip (*est. $17) kits are available. Fact Plus makes two types of kit. Fact Plus Select is a regular dip-stick-type test, where you hold the test strip in your urine stream. Fact Plus Pro uses a collection cup for the urine, then you expose the test strip in the collection cup.

e.p.t ( *est. $11 one strip , $16 two strips ) is a well-known brand that gets a lot of good reviews from consumers at Epinions.com, although many dislike the expense, and a few say the results aren't the easiest to interpret. e.p.t detects 40 mIU of hCG. Although popular with consumers and advertisers, this brand didn't hold up in product testing, because it's not as sensitive and is more difficult to interpret than First Response and Clearblue above. Like Clearblue, e.p.t has recently come out with a digital test that reads "pregnant" or "not pregnant." The digital version detects 50 mIU hCG, versus e.p.t Home Pregnancy Test which detects 40 mIU.

You might be wondering about store brands, since almost every discount store has them, including Target, Wal-Mart, K-Mart, Walgreens, and Osco, just to name a few. About.com's Pregnancy/Birth Guide, Robin Elise Weiss, recommends Wal-Mart's Equate brand (*est. $8, two-pack), saying, "It's a great, inexpensive pregnancy test kit," with separate control and testing windows and a cap to cover the absorbent tip. Equate is available in 25 mIU (white cap) and 100 mIU (purple cap), and reviewers warn to check carefully so you know which one you're getting. Some Equate samples failed to work in product testing, or took longer to work than stated by the manufacturer, but FertilityPlus.org has this to say: "The Equate brand switched manufacturers a couple of years ago. The older test had a significant online reputation for false positives, while the newer tests, manufactured by LifeCare, appear as reliable as most other brands (most brands get some reports of false positives). The main comment the test still gets is to beware of evaporation lines and read the test, like all brands, within the time limit listed in the instructions."

Many other store brands detect 40 to 50 mIU of hCG. FertilityPlus.org has a helpful comparison chart of each brand and detection levels, along with manufacturer information.

Important Features

Experts say to consider the following when buying a home pregnancy test:

• The most sensitive tests currently detect about 15 to 25 mIU of hCG, corresponding to detection of pregnancy within about a day of a missed period for 90% of women. For most women, the more sensitive, the better. If you have hCG in your system from miscarriage, recent birth or some fertility drugs, you might want to consider a less-sensitive test.

• "One-step" kits are generally considered the most convenient to use. Most can either be held briefly in the urine stream or dipped into a collection cup.

• Test results may be easier or more difficult to read, depending on the design. A fair degree of contrast between the line or symbol and the background is important. Evaporation lines can make the test more difficult to interpret. This is a common complaint with ALL pregnancy tests -- that interpretation is not foolproof, even with digital kits.

• If you think you may need a second test (for example, if your periods are irregular or you're testing very soon after a missed period), a double package is generally a better buy than paying separately for a second kit.

Our Consensus Report shows how many times products are top-ranked by reviewers included in our
All The Reviews Reviewed chart.

# of Picks	Model (with retailer links)	Details from Amazon.com
3	First Response (*est. $11)	details
2	Fact Plus (*est. $12.50)	details
2	e.p.t. (*est. $11)	details
1	Clearblue Easy Earliest Results (*est. $14)	details
1	Equate

First Response is top-rated by three reviewers, including the two best resources, for being the most sensitive test on the market. Fact Plus detects a higher amount of hCG (100 mIU), making it a good option for women prone to a false positive because of recent birth, miscarriage, or certain fertility drugs. Clearblue Easy Earliest Results comes in second in clinical trials to First Response. e.p.t sparks some complaints about difficult interpretation and detects 40 mIU of hCG, which isn't as sensitive as First Response and Clearblue, so we didn't include it in ConsumerSearch Fast Answers. Equate (Wal-Mart's store brand) is recommended in one review, although one of our top sources found some tests failed to work during product testing

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