A pregnancy test checks a woman’s blood or urine for the presence of a substance called human chorionic gonadotropin (hCG). This is a hormone made by the placenta.
Throughout pregnancy, the placenta provides the growing baby with oxygen and nutrients from the mother’s bloodstream. The levels of hCG in a pregnant woman’s blood and urine rise steeply during the first trimester, then fall to low levels for the rest of the pregnancy.
If you suspect you could be pregnant, you can see your doctor (or family planning clinic) for a pregnancy test. The doctor may perform a pregnancy test on your blood or urine. Alternatively, you could buy a home pregnancy test kit, which is available from pharmacists. However, always see your doctor for confirmation of pregnancy if you use a home kit.
Blood pregnancy tests used by doctors
Your doctor can give you a blood pregnancy test as early as 11–14 days after ovulation. To perform a blood pregnancy test, the doctor draws blood from a vein in your arm. This blood is sent to a laboratory for testing. The results of most blood pregnancy tests take at least a couple of days. The laboratory then advises the doctor of the result.
Blood test results are about 99 per cent accurate and can detect lower amounts of hCG than urine pregnancy tests. The two main types of blood pregnancy test include:
- Quantitative blood test – measures the exact amount of hCG in the blood and can give you an estimate of how far along the pregnancy has progressed.
- Qualitative blood test – only checks for the presence of hCG. Since this test doesn’t measure the exact levels of hCG, it can’t offer an estimate of gestation.
Urine pregnancy tests used by doctors
The doctor can give you a urine pregnancy test. You are asked to urinate into a plastic cup or something similar. The doctor then tests the urine using a kit that may look similar to a home pregnancy test kit.
Home pregnancy test kits
Home pregnancy test kits are available from pharmacists. These kits offer accurate readings (up to 97 per cent) if performed strictly according to the manufacturer’s instructions. However, many women who use home pregnancy test kits get inaccurate results.
The most common mistake is to test for pregnancy too soon after the missed period. The manufacturer’s instructions will tell you when is the best time to use the kit. It is very important to follow the manufacturer’s instructions exactly.
How to use a home pregnancy test kit
Home pregnancy test kits vary in their sensitivity to hCG. Most test kits are best used about one to two weeks after your period was due. Always strictly follow the manufacturer’s instructions. Generally speaking, most home pregnancy tests follow the same basic principles:
- You collect urine in a small container and dip the test strip into the urine. Alternatively, some kits offer a test strip that you hold under your stream of urine.
- To improve accuracy of results, it is best to test your urine when you first get out of bed. Early morning urine is concentrated and contains higher levels of hCG than at other times of the day.
- Most test strips indicate the presence of hCG by the appearance of a coloured line or dot.
- Results are rapid. Most test kits take only a few minutes to complete.
- Most kits come with a second test strip. This allows you to test again at a later stage.
Sometimes, a home pregnancy test may be positive when a woman isn’t pregnant. Common causes of false-positive results include:
- Dirty urine collecting cup (detergent residue, for example, is known to cause false-positive results)
- Faulty test kit (for example, the kit is damaged, past its use-by date or has been exposed to heat or moisture)
- Blood in the urine (from cystitis, for example)
- Protein in the urine (from kidney damage, for example)
- Certain medications including anti-convulsants, some fertility drugs, diuretics (fluid pills) and tranquillisers
- Recent birth or miscarriage, because a woman’s blood and urine may still contain detectible levels of hCG for a few weeks afterwards
- An ovarian tumour or some other type of hCG-producing growth.
Other reasons for a missed period
Pregnancy is not the only reason for a missed period. Other possible reasons include:
- Emotional stress
- Severe weight loss
- Severe dieting and exercising
- Particular drugs
- Menopause onset.
Sometimes, a woman may be pregnant but the home test kit gives a negative result. Common causes of false-negative results include:
- The test kit is used too early in the pregnancy and hCG levels are too low to be detected. Most test kits shouldn’t be used until your period is at least seven days late.
- The test is incorrectly timed. Use a kitchen timer or a watch with a second hand to be sure.
- The test is used incorrectly.
- The woman drank lots of fluids before taking the test and diluted her urine to the point where hCG levels are no longer detectible.
Always see your doctor for confirmation
If a home pregnancy test gives a negative result, yet you feel that you are pregnant:
- Trust your instincts.
- Treat yourself as if you are pregnant until proven otherwise.
- Avoid cigarettes and alcohol.
- Make an appointment with your doctor. Pregnancy tests performed in laboratories are 99 per cent accurate.
Inaccurate results from tests given by the doctor
Pregnancy tests taken by your doctor are rarely inaccurate. The occasional error is usually due to mistakes made in the laboratory. However, you can be reassured that the pregnancy test taken by your doctor is much more likely to be accurate than a home test you perform yourself.
Where to get help
- Your doctor
- Obstetrician and gynaecologist
- Family Planning Victoria Tel. (03) 9257 0100
Things to remember
- Many women who use home pregnancy test kits get inaccurate results.
- Follow the manufacturer’s instructions to the letter, and don’t test too soon after your missed period.
- Always see your doctor for confirmation of your pregnancy.
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