Nine out of 11 pregnancy tests sometimes tell women they’re not pregnant – when they are, new research reveals.
About 45 percent of pregnancies are unintended, and confirming a pregnancy is essential for women women’s decision-making and financial planning.
Taking a pregnancy test is stressful enough, but brands assure women that their at-home tests are ’99 percent effective,’ fueling the sale of some 20 million tests a year.
But all too often, they aren’t nearly as effective s they claim, a new Washington University, St Louis (WUSTL) found.
Researchers there found that nine out of the 11 top brands of at-home pregnancy tests could sometimes return false negatives – and the worst among them told women they weren’t pregnant when they were five percent of the time.
Women in the US buy some 20 million urine pregnancy tests a year. A new study found that the vast majority of pee tests trusted by hospitals can return false-negatives
So much hangs in the balance of the agonizing five-minute wait on the toilet to see if one or two lines appear on a pregnancy test.
At home pregnancy tests detect a fertilized egg via a hormone called human chorionic gonadotropin (HCG).
Within about two weeks of fertilization, a woman’s body starts producing HGC, the so-called pregnancy hormone, which is secreted by placenta cells even at early stages of the sacs’ formation.
HCG is an instruction for the uterine lining to stay in place to maintain the pregnancy, instead of being shed as would normally happen with a monthly period.
At home-pregnancy tests detect implantation by reacting to levels of a particular form of HCG called ‘intact HCG’.
But a fragment form of the hormone that exists only in the urine is up to 10 times more prevalent in urine beginning around the sixth week of pregnancy.
The fragment can effectively drown out intact HGC, meaning that the reactive chemicals in a pregnancy pee-stick won’t pick up on the decisive hormone.
Lead study author Dr Ann Gronowski saw this in her clinic a decade ago, she said in a WUSTL Q-and-A.
The clinic used a similar pregnancy test to what you might find in a pharmacy. A patient came in, took a test, got a negative result and returned home.
But she later called back. The woman was having spotting and cramping, symptoms she worried might mean she was miscarrying.
When she returned to the clinic, she was given a blood test for pregnancy and an ultrasound. She was pregnant – despite the results of the urine test even doctors had trusted.
Ever since, Dr Gronowski has been testing pregnancy tests.
Her work has led the Food and Drug Administration to require all new tests to return a positive result when the HCG fragment is high – not just the tried-and-true intact HCG.
But the rule doesn’t apply to previously approved pregnancy tests, which are still on shelves today.
In the latest round of testing, Dr Gronowski and her team looked at the top 11 tests used by hospitals to screen for pregnancy.
They found that seven of the tests might occasionally return false negatives, and two were likely to do so (or ‘highly susceptible’).
One of the poorly performing tests gave false negatives as much as five percent of the time, meaning that for every 20 women who took it, one might get a false negative result, and go home thinking she wasn’t pregnant when in fact she was.
That shoddy test was the very one Dr Gronowski and her colleagues had used to screen the patient who inspired the study for pregnancy (they’ve since switched to a more reliable test).
Only two of the 11 tests were nearly fool-proof.
In her interview, Dr Gronowski did not reveal which tests she and her team analyzed.
Dr Gronowski has seen a number of women post on pregnancy forms about trying at-home work-arounds.
‘Some women discovered our research and have been posting in online pregnancy forums, saying that if you think you’re pregnant but the test comes back negative, dilute the urine with water and try again because sometimes the tests are wrong,’ she said in the Q and A.
‘And that can actually work. Dilution reduces levels of the hormone fragment enough that the first antibody is more likely to detect the intact hormone again.
‘But I do not recommend this.’
Instead, Dr Gronowski says that if you have any doubts about the results of an at-home pregnancy test, schedule a blood test with your primary physician, OBGYN, or local hospital or clinic.