Pregnancy and ovulation: testing times

You may think you are pregnant, or you may be trying to conceive but just can’t seem to time it right. Easy-to-use home test kits are available to tell you if you are pregnant or when you have the best chance of conceiving. This article looks at the different tests and how they work.

Home pregnancy testing

Home pregnancy test kits detect the presence of the hormone human chorionic gonadotrophin (hCG) in the urine. The woman’s body begins to secrete hCG when an egg is released from the ovaries and fertilised. This secretion increases rapidly through the first trimester of pregnancy; doubling every one or two days for about 10 to 12 weeks, then usually reducing to a stable level once the placenta is established and throughout the rest of the pregnancy.

Ovaries respond to hCG by secreting high levels of the hormones oestrogen and progesterone. This helps maintain the pregnancy.

Tests can be taken either by holding a strip in the flow of urine while on the toilet (midstream test) or by collecting a urine sample and dipping the strip into it (dipstick).

How accurate are home pregnancy tests?

Most tests results are around 99% accurate, as long as they are completed according to the manufacturer's instructions.

What causes a false-positive pregnancy test result?

A false-positive test result is when a test says you are pregnant but in fact you are not. Medicines such as fertility drugs, which contain hCG, are a common cause of a false-positive pregnancy test.

Spontaneous abortions can occur early in pregnancy, leaving measurable hCG levels, which will also give a false-positive result. Some hCG may be found in urine for up to eight weeks after a miscarriage or termination, or for up to four weeks after childbirth.

Pregnancy tests are not affected by alcohol, pain relief medicines, antibiotics or the oral contraceptive pill.

Ovulation testing

The release of eggs from the ovaries is controlled by luteinising hormone, which increases about 24 to 36 hours before ovulation. Most home ovulation tests detect the surge in luteinising hormone by measuring the levels in a woman's urine - this is used to identify the peak fertility days.

One home ovulation test kit relies on the user interpreting the appearance of her dried saliva under a microscope. According to the manufacturer, dried saliva has the appearance of pebbles or dots under a microscope when the woman is not ovulating. Dried saliva from a woman who is ovulating, however, crystalises into a fern-like pattern. In the two to three days before she ovulates, the saliva contains a combination of both. Note: dried saliva taken from a woman around the time of her period can also crystalise into a fern-like pattern, but does not indicate that she can conceive at this time.

Traditional methods of home ovulation monitoring methods have involved the less accurate and often impractical methods of measuring basal body temperature (BBT) and the consistency of cervical mucus. The mucus lining the cervix is normally a thick consistency but it becomes thin during ovulation to help the passage of sperm towards the egg. A woman’s BBT rises by about 0.5 degrees celsius just after ovulation takes place. To find that small but sustained rise the woman must record her body temperature every day until the rise occurs. This indicates the time in the cycle when ovulation is most likely to occur.

Unlike these traditional methods of detecting ovulation, home ovulation testing kits provide an indication of ovulation in advance, rather than during or after the event. This gives you more opportunity to get pregnant.

For further advice about conception and pregnancy, visit our Pregnancy Centre.

Original material provided by Auckland pharmacist Jane Caldwell. Copyright material. Reproduced from Pharmacy Today magazine, with kind permission, and updated by everybody in May 2009. (With thanks to Mark and Amy Swearingen for positive pregnancy test image.)