Pregnancy Test Guide
Medically reviewed on Mar 11, 2013 by L. Anderson, PharmD.
There are two different types of pregnancy tests: those that check the blood and those that check the urine. The pregnancy blood (serum) test must be performed at a doctor’s office or clinic, but the urine test can be performed at home or a clinic. Many woman like the convenience and privacy of using an at home pregnancy test to initially determine if they are pregnant or not. Home pregnancy tests are very accurate (if used properly), inexpensive and easily available. If a pregnancy test is found to be positive, or if it is negative but the woman still suspects she might be pregnant, she should immediately seek the advice of a health care provider.1
What early pregnancy symptoms or pregnancy signs may occur?
The first sign of pregnancy that many women experience is a missed menstrual cycle (period). Other early symptoms of pregnancy or signs of pregnancy might be:
- nausea and vomiting (or morning sickness, which can really happen at any time of the day or night)
- tender or swollen breasts
- increased urination, especially at night
- fatigue and tiredness
- food distastes or food cravings
How do pregnancy tests work and how should they be used? How accurate are home pregnancy tests?
All pregnancy tests work by detecting the presence of human chorionic gonadotropoin (hCG), the pregnancy hormone.
In both urine and blood pregnancy tests, the presence of the hormone human chorionic gonadotropoin (hCG) is evaluated. The hCG hormone is usually only present in blood or urine if a woman is pregnant. When an egg fertilized with sperm is implanted in the uterus of the woman the hCG is then produced. The egg usually implants into the wall of the uterus about six days after fertilization, but in about 10 percent of women implantation may not occur until after the first day of the missed period. The levels of hCG rise in the body early in pregnancy after implantation occurs.1
It is usually best to wait one week after a missed period before using a home pregnancy test.
While many early detection pregnancy tests claim to be 99 percent accurate even one day after a missed period, results can be variable. In up to 10 percent of women, implantation may not occur until after the first day of the missed period, in which case hormone levels of hCG may not be high enough to be detected by the test. However, research shows that most home pregnancy tests can detect hCG accurately one week after a missed period. Also, testing in the morning with the first urination may boost the amount of hCG in the sample.
A quantitative blood pregnancy test done at the doctor’s office (also known as the beta hCG test) can detect low levels of hCG and measure the actual quantity of hCG in the body; this test may be the most accurate option if a woman needs a very early pregnancy test. In terms of ovulation, a blood pregnancy test can be accurate six to eight days after ovulation, while a urine test is usually accurate about 14-21 days after ovulation. Women should contact their physician if they prefer the beta hCG test.
If a negative pregnancy result occurs with a home urine test, the test should be repeated in a few days to confirm the negative result. Women with positive pregnancy tests should contact their doctors for an appointment.
Check the expiration date, read the instructions, and follow the specific directions for each home pregnancy test package. Store unopened tests in a cool, dry place.
Before a home pregnancy test is purchased, the expiration date should be checked on the outside of the packaging. If the expiration date is passed, do not buy or use the pregnancy test. While home pregnancy tests work in the same way by detecting hCG in the urine, the specific directions for use may vary from test to test. Be sure to read and follow the instructions exactly.
Most tests have a “control” and a “result” window, or a digital display
Some tests instruct the user to hold the test stick in the stream of urine, while others involve dipping the stick or pregnancy test strips into a cup of collected urine. It is important to wait the correct number of minutes instructed on the package before the results are read.
Most urine pregnancy tests have a “control” window and another window that is the “results” window. When this line or other symbol appears in the control window it ensures that the test is working properly. If a control window does not show a line or other symbol as indicated by the package instructions, then the test is not working properly. A new pregnancy test should used the next morning.
If the control window is working properly, and a line, plus sign, or other symbol as directed by the package instructions appears in the results window, this means the test is positive and the woman is pregnant. For positive results, the woman should contact her physician to make an appointment to initiate prenatal care. If no symbol appears in the window as directed by the instructions, then the results are most likely negative. However, it is best to confirm the results of a negative test by repeating it in a few days. A faint symbol on the pregnancy test window is usually still positive; it may mean that the levels of hCG in the blood are are still quite low. If a woman is concerned about a faint line on a pregnancy test, it is best to wait a few days and repeat the test, or contact a physician for a confirmatory blood test.
Some digital pregnancy tests now have a digital display window that will report the results in words, such as “pregnant” or “not pregnant”. Digital pregnancy tests may not have a control window, but may show a flashing symbol in the window prior to the result.
Most home pregnancy tests come with a toll-free number to call if the woman has questions.
Where can home pregnancy tests be bought, which brands are common, and what are the costs?
Home pregnancy tests are readily available without a prescription and most are very affordable
Home pregnancy tests can be bought without prescriptions at most pharmacies, grocery stores and larger retail chains. Women can buy also a pregnancy test online over the Internet, but women should be sure they are buying from a reputable online retailer and always check the expiration date on the outside of the package once the test is received in the mail. If the expiration date has passed, do not open the test and return it to the retailer for a full refund.
Brand name home pregnancy tests are available in addition to the less expensive store brands such as Equate. More common brand names of home pregnancy tests include: Answer Pregnancy Test, BabyConfirm Pregnancy Test, Clear Blue Pregnancy Test, Clearblue Easy Pregnancy Test, EPT Pregnancy Test, Fact Plus Pregnancy Test, First Response Pregnancy Test, and New Choice Pregnancy Test. Many packages may also contain more than one test, which drive up the costs. On average, home pregnancy tests cost between $5 and $40 depending upon the brand and contents.
A study in 2011 evaluated the utility of six home pregnancy tests. Pregnancy test sensitivity and specificity was also studied. Researchers found that the hCG sensitivity of the First Response manual and digital pregnancy tests was 5.5 mlU/mL, while the sensitivity of the EPT and Clear Blue brand was 22 mlU/mL. According to the authors, both First Response tests detected 97 percent of 120 pregnancies on the day of the missed period. The EPT manual and digital devices detected 54 and 67 percent of pregnancies, respectively, and the Clear Blue manual and digital devices detected 64 and 54 percent of pregnancies, respectively, on the day of the missed period.2
What is meant by a false positive pregnancy test or a false negative pregnancy test?
A false positive is when the results of the pregnancy test indicate that the woman is pregnant, but she is not. A false negative pregnancy test is when the results of the test indicate that the woman is not pregnant, but in actuality, she is pregnant. A false-negative is much more likely to occur than a false-positive.1
What can lead to a false positive pregnancy test?
In rare circumstances, the hCG hormone may be present in the body when a woman is not pregnant and may lead to a pregnancy test false positive result. Some infertility medications (medications that are used when a woman is having trouble getting pregnant) may cause a false-positive because they contain hCG. Ovarian cysts, recent pregnancies, an ectopic or molar pregnancy or menopause may also lead to false positive results.3
What can lead to a false negative pregnancy test?
Reasons for a false negative pregnancy test may include performing the test too early, timing the test wrong, or using a dilute urine. To help avoid false negative results, wait for one week after a missed period to use the pregnancy test, use a timer or stopwatch to increase pregnancy test accuracy, and use the first urine of the morning for the test, when the concentration of hCG is at its highest level.1
Can other substances, such as medications or alcohol, interfere with the results of a home pregnancy test?
Most medications, including birth control pills and antibiotics, do not interfere with pregnancy test results. Alcohol and illegal drugs, such as marijuana, cocaine or heroin do not interfere with the results of a pregnancy test, but these substances should not be used if a woman is trying to conceive, is pregnant or is sexually active without a reliable form of birth control.3
- Cole LA. The utility of six over-the-counter (home) pregnancy tests. Clin Chem Lab Med. 2011;49:1317-22.
- Mayo Clinic Staff. Home pregnancy tests: Can you trust the results? http://www.mayoclinic.com/health/home-pregnancy-tests/PR00100 Accessed 02/06/2012.