Pregnancy testing

How do pregnancy tests work?

A pregnancy test checks your blood or urine for a hormone called human chorionic gonadotropin (hCG). This is a hormone made by the placenta (the placenta provides your growing baby with oxygen and nutrients from your bloodstream throughout the pregnancy). The amount of hCG in your blood and urine rise steeply during the first 12 weeks of pregnancy and then fall to low levels for the rest of the pregnancy.

Home pregnancy test kits

Home pregnancy test kits are available from pharmacists. These kits offer accurate readings (up to 99 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.

Positive result

If the test is positive (no matter how faint the line, colour or sign is), you should see your GP (doctor) (or family planning clinic) to confirm the result with a blood test or another urine test. Be aware that false-positive and false-negative results can happen.

False positive: Although rare, this can happen if you have blood or protein in your urine. Certain drugs can also cause this (tranquilisers, anticonvulsants, hypnotics and fertility drugs). Other reasons for false results are:

• 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)
• 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.

Negative result

If you get a negative result, you are probably not pregnant BUT false-negatives can happen if:

• you didn’t follow the instructions correctly
• the test is out-of-date
• you tested too soon after the pregnancy began
• your urine was too diluted
• you are taking certain medicines, including antihistamines.

If you suspect you may be pregnant, see your doctor and ask for a blood pregnancy test to confirm the result.

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.

Blood pregnancy tests used by doctors

Your doctor can give you a blood pregnancy test as early as 11 to 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.

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.

Other reasons for a missed period

Pregnancy is not the only reason for a missed period. Other possible reasons include:

• breastfeeding
• emotional stress
• severe weight loss
• severe dieting and exercising
• obesity
• particular drugs
• menopause onset.

Where to get help

• Your GP (doctor)
• Obstetrician-gynaecologist
• Pharmacist
• Sexual Health Victoria (SHV). To book an appointment call SHV Melbourne CBD Clinic: (03) 9660 4700 or call SHV Box Hill Clinic: (03) 9257 0100 or (free call): 1800 013 952. These services are youth friendly.