According to a new study from the American Association for Clinical Chemistry, 9 out of 11 of the most popular hospital urine pregnancy tests are more likely to produce a false-negative result after the fifth to seventh week of pregnancy, even though the tests perform well in the first month after conception.
Led by Ann M. Gronowski, PhD, of the Washington University School of Medicine, St. Louis, the study shows that when a woman's egg is fertilized, it begins producing the hormone human chorionic gonadotropin (hCG), which is detected in urine or blood. However, during the fifth to seventh week of gestation, urine concentrations of an hCG variant known as the hCG beta core fragment increase rapidly, interfering with hCG detection. This is what causes false-negative test results.
In a hospital, the failure to detect a false-negative can lead to serious consequences , like administration of medications that cause birth defects or failure to diagnose ectopic pregnancy, which is the leading cause of first-trimester pregnancy-related maternal death.
Ann's team found these results after testing a method that evaulated the ability of hospital pregnancy tests to detect hCG when high concentrations of hCG beta core fragment are also present.
"There are three important take-home messages here," Ann says. "One, physicians, nurses, and other health care professionals need to be educated that this is a problem. Two, manufacturers need to make the possibility of false negatives clearly visible in their package inserts and work to develop better tests. And three, in centers where quantitative blood hCG testing is available, this should be the preferred pregnancy test. Blood testing is not subject to this effect because hCG beta core fragment is not present in serum."
Conversely, most at-home pregnancy tests are accurate 99 percent of the time when taken one week after a missed period. According to the Mayo Clinic, a false-negative result on an at-home pregnancy test can occur when the test is taken too early, the test results are checked too soon or if you don't take the test first thing in the morning if your urine is diluted.
Do you trust at-home pregnancy tests more than hospital pregnancy tests?