What is a pregnancy test?
Pregnancy tests are designed to detect a special hormone that is only present when a woman is pregnant. This hormone, known as human Chorionic gonadotropin (HCG), is produced by the placenta when a female ovum (egg) has been fertilized by a male spermatozoa (sperm) and implants in the female’s uterus. This occurs, on average, about six days after the egg and sperm come together. The level of HCG increases as the pregnancy progresses. However, six days is merely an average- for some women, implantation does not occur until days later.
Pregnancy tests can detect HCG in both urine and blood. While some women prefer to go to the doctor for a blood test to determine whether they are pregnant, many women prefer to perform a pregnancy test in the comfort and privacy of their own bathroom. These tests, available commercially, are very accurate for the most part when used at the right time. Home pregnancy tests (HPTs) are most accurate when used one week after a missed menstrual period. However, as mentioned previously, some women do not experience implantation until a later time. These women, a smaller percentage, are indeed pregnant, but their HPT may be negative. This can cause some confusion and worry. 
There are a few situations that can influence a false negative pregnancy test, for example:
- - if you do a pregnancy test too early, you could still be pregnant, because there may not be enough HCG in your body to give a positive test result. If you, however, still think you're pregnant, you can perform a pregnancy test a few days later.
- - some medications can affect pregnancy results, these medications include :
- allergy medications, such as promethazine
- drugs that are used with Parkinson's disease
- hypnotics aka sleeping pills
- diuretics — drugs that increase the amount of urine produced — these medications are used to treat conditions such as heart failure
- anticonvulsants, drugs that treat epilepsy and other seizures or fits)
- some drugs that are used for infertility
How should a pregnancy test be used?
In order to ensure accuracy, pregnancy tests should be used correctly. Always read the instructions included with an HPT and follow all directions carefully. Although some tests advertise that they can accurately detect pregnancy as early as one day after a missed menstrual period, this is not always the case. In addition, some tests may be more sensitive than others.
Follow the tips below to ensure accuracy:
- Read the expiration date- a test whose expiration date has passed may not be accurate. The expiration date should be located on the box, so check before you buy!
- Wait the directed amount of time before reading your result- waiting for your HPT result may feel like the longest period of time you will ever spend, but research shows you should wait 10 minutes before reading your result to ensure accuracy.
- Perform the test first thing in the morning- the amount of HCG in your urine may be highest in the morning, according to some research. Do the test immediately upon awakening, when urine has been present in your bladder for a while.
- Resist testing too early- as mentioned, many tests state that they can detect pregnancy accurately as early as one day after a missed period, but research has suggested that, for some women, HCG levels may still be too low to detect at this point. Wait until one week after a missed period to avoid a false-negative result.
- Be sure you know how to read the test- read the instructions on your HPT carefully before performing the test. Know how to interpret the test windows. Some will show a plus sign, some will use the word “pregnant” to indicate a positive result, and others will use one line or two. In addition, be sure that the control window, which is used to ensure test validity, shows the result it is supposed to according to test directions. If the control window does not perform as it should, the test is not accurate.
What do I do if the test is negative and I have missed a period?
Because woman’s cycles are different lengths and ovulation can occur at different times for different women, and the egg can implant at varying times in a woman’s uterus, some women will have a negative pregnancy test when they test a week after they have missed a period and will still be pregnant. Experts suggest that women who have a negative pregnancy test should test again in a week, as HCG levels may not have reached a high enough level to be detectable. If the test is again negative, the woman should see her doctor.
There are other early signs of pregnancy that a woman may experience that may clue her into her pregnancy, in addition to a missed period. These signs and symptoms are often very subtle in early pregnancy and can be mistaken for the symptoms of other conditions :
- Breast tenderness- breasts (and sometimes nipples) may feel very tender and may swell, just as they often will during some women’s menstrual periods. Some women experience breast tenderness as a very early sign of pregnancy.
- Fatigue- although some women will not experience fatigue until later in their pregnancy, some women notice fatigue very early in their pregnancy.
- Frequency- some women experience urinary frequency early on as their uterus begins to grow, placing pressure on the bladder and necessitating frequent trips to the lady’s room.
- Nausea and vomiting- this may be the earliest sign of pregnancy for some women and can persist for many weeks. Nausea is often worse in the morning upon awakening or when the stomach is very empty.
- Mood swings- altered hormone levels may cause your moods to be somewhat unstable for a while! You may find yourself laughing one minute and crying the next. No need to panic- this is normal and will pass. (If it doesn’t, or you find yourself feeling sad much of the time, see your physician).
- Fainting- some women experience dizziness and/or faintness in early pregnancy, particularly if they skip a meal. They may attribute this to skipping breakfast, without realizing they are pregnant and their growing baby is using up all of their available energy.
- Increased temperature- women who are TTC (trying to conceive) may be charting their temperature to determine when they ovulate. Their temperature may stay elevated for several days when they become pregnant. Women who have not been charting their temperatures may just find that they feel warmer than normal much of the time.
- Bloating and weight gain- some women may attribute the bloating of early pregnancy with overeating. Weight gain can begin almost immediately for some women. If you are gaining weight and have missed a period, there is a strong possibility you are pregnant and you should retest if your pregnancy test was negative!