- False-Positive Results
- Urine/Blood Tests
- When to See a Doctor
A home pregnancy test detects the presence of human chorionic gonadotropin (hCG), which is produced in a pregnant woman. Traces of hCG can be seen in urine 3-4 days after the fertilized egg implants in the uterus, and the amount doubles every 48 hours. When there is enough hCG in the body, a pregnancy test can detect it and produce a positive result.
If your periods are irregular, however, and your test result is negative, you should repeat a home pregnancy test after 1 week.
How accurate are home pregnancy tests?
Home pregnancy tests are quite reliable and usually 99% accurate. However, it is critical to carefully follow the instructions on the package.
- It is recommended to test your urine in the morning since hCG levels will be at the highest concentration as soon as you wake up.
- You can take the test at any hour of the day, but you need to keep your bladder full for at least 4 hours prior to the test.
- Avoid drinking too much water before the test because it can dilute the hCG levels in your urine.
Here is how the tests work:
- The test kits come with a test stick and a container that is used to collect the urine and transfer a few drops to the test stick.
- If you are pregnant and there is sufficient hCG in your urine, the hCG in your urine reacts with the anti-hCG antibodies present in the test stick and inactivates them.
- As anti-hCG bodies are inactivated, the stick indicates a positive pregnancy test.
What can cause a false-positive pregnancy test result?
In rare cases, a false-positive outcome can be caused by:
- Blood or protein in your urine
- Early miscarriage
- Certain medications, such as tranquilizers, anticonvulsants, hypnotics, and fertility drugs
Other reasons for a false-positive result include:
- Molar pregnancy: Also called a hydatidiform mole, a molar pregnancy is a benign growth that develops abnormally after an egg is fertilized. The placenta develops into an aberrant mass of cells and cysts. In rare cases, an embryo develops but is deformed and will not survive. In some cases, no embryo exists at all. Molar pregnancies can have serious complications and must be treated by a specialist.
- Ectopic pregnancy: Ectopic pregnancy occurs when the fertilized egg implants in a location other than the uterus. In a tubal pregnancy, this occurs in one of the fallopian tubes that connects the ovaries to the uterus. However, the egg can sometimes implant in the abdominal cavity, ovary, or cervix. Because the fertilized egg cannot survive in these locations, the pregnancy cannot progress normally and the growing tissue can harm the mother's internal tissues, resulting in dangerous complications such as life-threatening blood loss. Early treatment of an ectopic pregnancy is critical.
- Chemical pregnancy: Women who get early positive pregnancy test results but then get their period may have a chemical pregnancy. This is a situation in which the fertilized egg implants normally in the uterus, but only long enough to begin generating hCG. The egg then ceases growing for unknown reasons. This form of early miscarriage usually occurs when the fertilized egg has a flaw that prevents it from maturing normally. According to some experts, 20%-30% of all pregnancies end in miscarriage.
What tests are done to confirm pregnancy?
In addition to false-positive results, a home pregnancy test may show a false-negative result, especially if you tested too early or if the kit was defective.
In order to confirm the results of a home pregnancy test, talk to your doctor to undergo additional tests. Your doctor may order urine or blood tests:
- Urine tests: Urine is tested for the presence of hCG. A diluted sample may produce a false-negative result.
- Blood tests: Blood tests are more sensitive than urine tests and can give an accurate result 9-10 days after conception. Blood test results not only confirm the pregnancy but can also diagnose a potential miscarriage. There are two types.
- Qualitative test: Confirms the presence of the hCG hormone in the blood
- Quantitative test: Measures the amount of hCG present in the blood.
- Higher hCG levels may indicate a multiple or twin pregnancy
- Lower hCG levels may indicate a miscarriage
- Slow rise of hCG levels may indicate an ectopic pregnancy
If pregnancy is confirmed, an abdominal ultrasound can be done to assess the development and health of the fetus.
When should you see a doctor?
Regardless of your pregnancy test results, consult your doctor if you develop any of the following symptoms:
- Abnormal vaginal bleeding
- Severe, stabbing pain in the abdomen or on one side of the pelvis
- No period even after multiple negative home pregnancy test results
- Persistent pregnancy symptoms even after negative test results, such as:
If your home pregnancy test result is positive, you should see your doctor to both confirm the pregnancy and begin prenatal care.
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American Pregnancy Association. What is HCG? https://americanpregnancy.org/getting-pregnant/hcg-levels/
Betz D, Fane K. Human Chorionic Gonadotropin. [Updated 2021 Aug 11]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2022. https://www.ncbi.nlm.nih.gov/books/NBK532950
Memon N. How Soon Will a Pregnancy Test Read Positive? MedicineNet. https://www.medicinenet.com/how_soon_will_a_pregnancy_test_read_positive/article.htm
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