Each year, women in the U.S. rely on some 20 million home pregnancy tests to learn potentially life-altering news. Despite marketing claims that such tests are 99 percent accurate, research at Washington University School of Medicine in St. Louis over the past decade has shown that up to five percent of pregnancy tests return results indicating a woman is not pregnant when, in reality, she is.
Makers of pregnancy tests advise that tests taken in the first week or two after conception could be inaccurate because pregnancy hormones may not have risen high enough to be detected. But Ann Gronowski, professor of pathology and immunology, and of obstetrics and gynecology, and medical director of core laboratory services at Barnes-Jewish Hospital, discovered that pregnancy tests can also give incorrect results to women five weeks or more into their pregnancies, when hormone levels tend to be very high. She published the first paper describing this problem in 2009, and since then has continued studying and raising the alarm on this serious but under-recognized issue. Recently, she and colleagues published a paper in the journal Clinical Chemistry, in which they evaluated how likely several pregnancy devices were to give false negative results.