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A pregnancy test kit works by detecting the amount of human chorionic gonadotrophin (hCG) in urine. Associate Professor Tan Thiam Chye, Head and Senior Consultant, Inpatient Service, Department of General Obstetrics and Gynaecology, KK Women’s and Children’s Hospital (KKH), a member of the SingHealth​ group, explains more.

How accurate are pregnancy test kits?

A pregnancy test kit is rarely wrong. It is more than 99 per cent accurate. Thus, if your test is negative, it means that you are not pregnant; However, if you are very early in your pregnancy and the test is done far too early, there could be an insufficient amount of urine hCG for the test to detect.

“So, if a test comes back negative but you strongly suspect that you are pregnant, repeat the test in a few days’ time,” says A/Prof Tan.

There are rare examples when the hCG level is raised transiently and then drops to zero. This is known as a “biochemical pregnancy” and could be the cause of a false positive result of the test kit. However, this initial rise of the hCG level will soon drop in a “biochemical pregnancy” and result in a negative urine pregnancy test.

“In a ‘biochemical pregnancy’, vaginal bleeding will occur soon after, which will coincide with ‘delayed menses’,” says A/Prof Tan. ”Rarely, there could be ovarian tumours which secrete hCG and the false positive result could be wrongly interpreted as a pregnancy.”

Pregnancy test kits: Frequently asked questions

  1. Do I have to test with first morning urine?
    Although you can test any time of the day, your first morning urine specimen is usually the most concentrated of the day and would have the most pregnancy hormone in it.
  2. When should I take the test if I suspect that I am pregnant?
    You can test your urine as early as six days past ovulation, but the first day of your missed period is recommended for greatest accuracy.
  3. Do I need a blood test for hCG to confirm my pregnancy?
    Blood tests for hCG are more accurate and they can also measure the actual levels of the hormone. These tests may be useful to differentiate a miscarriage when the blood hCG will drop with time, or a healthy pregnancy when the blood hCG level will double every two days. “Occasionally, we need to follow-up the hCG levels to help us diagnose early ectopic pregnancy (pregnancy outside the womb), which could be potentially life-threatening,” says A/Prof Tan.

"The New Art and Science of Pregnancy and Childbirth", a pregnancy book written by A/Prof Tan Thiam Chye, Dr. Tan Kim Teng, Dr. Tan Heng Hao, A/Prof John Tee Chee Seng. KK Women's and Children's Hospital (KKH), a member of the SingHealth group.

* Available at all major book stores and Pharmacy in KKH.

Find out how pregnancy test kits work on the previous page.

Ref: S13​