Conflicting pregnancy test results are common and can be confusing. Understanding how pregnancy tests work and the factors influencing their accuracy can clarify why discrepancies occur. This article provides guidance on what might be happening and the next steps to get a definitive answer.
Understanding Pregnancy Tests
Pregnancy tests primarily function by detecting human chorionic gonadotropin (hCG), a hormone produced after a fertilized egg implants in the uterus. This hormone begins to be produced around 6 to 10 days after conception. As pregnancy progresses, hCG levels rapidly increase, typically doubling every 48 to 72 hours in the early weeks.
There are two main types of pregnancy tests: at-home urine tests and laboratory blood tests. Urine tests detect hCG in urine, often displaying a line, symbol, or word for a positive result. Blood tests, performed by a healthcare provider, offer more detailed information. Qualitative blood tests detect hCG presence, while quantitative blood tests measure the exact amount, providing a numerical value.
Test sensitivity refers to the lowest concentration of hCG a test can detect, measured in milli-international units per milliliter (mIU/mL). Lower numbers indicate higher sensitivity and earlier detection. For instance, a 10 mIU/mL test detects pregnancy sooner than one requiring 25 mIU/mL. This difference in sensitivity is a common reason for varying results, especially in early pregnancy when hCG levels are still low but rising.
Common Reasons for Discrepancies
Conflicting pregnancy test results often stem from factors related to the timing of the test or how it was performed. One common reason is testing very early in pregnancy when hCG levels are just beginning to rise. A highly sensitive test might detect these low levels, showing a faint positive, while a less sensitive one might still show negative. Since hCG levels increase rapidly, retesting after a few days can often yield a clearer result.
Differences in test sensitivity between brands can lead to varied outcomes; one test might require a lower hCG concentration for a positive result compared to another. Diluted urine, from consuming large amounts of fluids, can also lower hCG concentration, potentially causing a negative result even if pregnancy is present. Using first-morning urine is often recommended because it is typically the most concentrated.
User error is a frequent cause of discrepancies. Not following test instructions precisely, such as reading the result outside the recommended time frame, can lead to inaccurate readings. Reading the test too late can result in an “evaporation line,” a faint, colorless streak that appears as the urine dries, which can be mistaken for a positive. Unlike a true positive line, which has color and appears within the specified reading window, an evaporation line is typically gray or colorless.
A “chemical pregnancy” is a very early miscarriage where a fertilized egg implants and briefly produces hCG, leading to a positive test, but then stops developing. In such cases, hCG levels may rise enough to trigger a positive test but then decline, resulting in a subsequent negative test.
In rare instances, certain medications, particularly fertility treatments containing hCG, can lead to a false positive result. Certain medical conditions like urinary tract infections, some ovarian cysts, or very rare cancers can also cause elevated hCG levels, though this is uncommon.
What to Do Next
If you receive conflicting pregnancy test results, re-testing is the most practical next step. Wait at least 48 to 72 hours before re-testing, allowing sufficient time for hCG levels to rise significantly if you are pregnant. Using first-morning urine can increase accuracy, as it typically contains the highest hCG concentration. Consider using a different brand of test for confirmation, as sensitivities can vary.
Follow the instructions provided with the pregnancy test kit. Pay close attention to the recommended reading window, and do not interpret results after this time to avoid confusion with evaporation lines. Understanding that a faint line appearing within the reading time is typically a positive result, regardless of its intensity. If results remain unclear, or if you have concerns, observing your body for developing pregnancy symptoms or the onset of your period can provide further clues.
When to Consult a Healthcare Provider
Consult a healthcare provider if you continue to experience conflicting pregnancy test results after re-testing. A healthcare provider can offer definitive confirmation of pregnancy through a blood test, which measures the exact amount of hCG and tracks its rise. They can also perform an ultrasound, confirming pregnancy and assessing its location and viability once hCG levels reach 1,000 to 2,000 mIU/mL.
Consult a healthcare provider if you have missed a period but consistently receive negative home tests, or if you are experiencing pregnancy symptoms without clear test results. They can evaluate symptoms, rule out other medical conditions, and provide personalized guidance. If there is concern about an early pregnancy complication, such as a chemical pregnancy or an ectopic pregnancy, a provider can offer accurate diagnosis and appropriate management.