Taking a home pregnancy test can trigger many emotions -- excitement, anxiety, and if you’ve been unfortunate in receiving a negative test result after a negative test result, frustration and anger. False negative pregnancy tests are much more common than false positives. While a urinary tract infection (UTI) is unlikely to cause a false negative it could do so, at least in theory. If you have a UTI, see a doctor and then retake the test a few days later.
Pregnancy Tests 101: Understanding How They Work
To understand false pregnancy test results, including false negatives, you need to understand how pregnancy tests work. Pregnancy tests look for one thing, and one thing only: the hormone HCG. All women have very low levels of HCG in their body, but during pregnancy, this hormone increases rapidly. So home pregnancy tests look for higher than normal HCG levels in urine. Because home tests are not sensitive enough to detect very low HCG levels, they are unlikely to give a false positive.
So to detect pregnancy, a person must have enough HCG in her urine. This depends on several factors:
- How far along she is in her pregnancy. The body only begins producing HCG after the egg implants in the uterus, not when the egg is fertilized. From there, HCG levels rapidly increase. Therefore, waiting longer is more likely to get an accurate result.
- How concentrated the urine is. First morning’s urine tends to have the highest levels of HCG.
- Whether anything has contaminated the urine or the test.
- How sensitive the test is. More sensitive pregnancy tests can get an earlier result. However, almost all tests are capable of getting a positive result within a day or two of a woman’s missed period.
A home pregnancy test will not measure other hormones or chemicals in the urine, so most medications, infections, or medical conditions are unlikely to affect home pregnancy tests unless they also affect the composition of the urine.
Sometimes, when a woman has a very early miscarriage, HCG levels rise rapidly and then fall. This can cause a positive test, followed by a negative test.
Can a UTI Cause a False Negative Pregnancy Test?
It is very unlikely that a urinary tract infection would cause a false negative pregnancy test. And it is completely safe to use a home pregnancy test with a urinary tract infection. It is, however, theoretically possible that in some cases a UTI might alter the results of a home pregnancy test.
This could happen if:
- A woman develops an infection so severe that other chemicals dilute the urine, making it difficult for a pregnancy test to detect HCG.
- A UTI makes it difficult for a woman to control the flow of her urine. Some UTIs can even cause a woman to have accidents. This can cause her to urinate too much on the pregnancy test stick, diluting the sample. Instead, try peeing in a cup and dipping the stick in the cup for the time recommended on the test package.
- A woman uses antibiotics or other drugs that change the composition of the urine. There is no medical evidence that antibiotics that treat UTIs change urine composition, but it’s still theoretically possible.
- A woman drinks large volumes of water or other fluid in an attempt to flush out the infection. Very early in pregnancy, when HCG levels are very low, this could dilute the urine, making it more likely that a woman gets a false negative.
However, these scenarios are very rare. The more pressing concern is that a UTI can have serious and even catastrophic effects on a woman’s health. Left untreated, a UTI can spread to the kidneys and to other organs. Especially early in pregnancy, this can endanger a developing baby. Untreated infections increase the risk of genetic mutations, early miscarriage, pregnancy complications, and a host of other issues. Taking care of your body when you are pregnant or think you might be is the best thing you can do for your baby.
UTI antibiotics are safe to use during pregnancy and are absolutely safer than allowing a UTI to go untreated. So seek medical care as soon as possible, and be sure to tell your doctor if you think you might be pregnant. While home remedies such as cranberry juice and over-the-counter pain relievers may temporarily help with symptoms, they will not treat the underlying infection. So don’t just rely on home remedies. See a doctor as soon as you can.
Common False Negative Pregnancy Test Causes
While a UTI is unlikely to cause a false negative pregnancy test, many other factors can.
Some common reasons for a false negative test include:
- Not waiting long enough after ovulation.
- Using urine that is not sufficiently concentrated. Especially if you’re testing early, it’s best to use the first morning’s urine.
- Using an expired test.
- Not following test instructions.
- Using a test that is not sensitive enough. If you test early, choose the most sensitive test available.
- An early miscarriage. If you are pregnant and having a miscarriage, HCG levels fall rapidly, especially in the early days of pregnancy. It’s possible that you got a negative result because you were pregnant, but your body is already miscarrying.
Can a UTI Cause a False Positive?
Just as a UTI is unlikely to cause a false negative, it is unlikely to cause a false positive. In fact, the odds of a false positive are much slimmer than a false negative, including with a UTI. So a woman with a UTI who gets a positive test should assume she is pregnant, and promptly treat the infection.
So what can cause a false positive test? A false positive usually only happens for a couple of reasons, including:
- Using an expired test, or not following the instructions on the test.
- Waiting too long to read the test results. This can cause an evaporation line to appear, which may look like a positive test.
- Taking fertility drugs that increase HCG levels.
- Certain hormonal abnormalities -- that your fertility specialist should be able to diagnose.
- A very early miscarriage. Sometimes called a chemical pregnancy, this happens when a woman has a miscarriage before a doctor detects pregnancy. A positive test followed by a negative test is not usually a false positive. Instead, it typically means the woman had a miscarriage -- especially if she began bleeding shortly after the positive test.
- A recent miscarriage. If you’ve had a miscarriage in the last month or two, especially if the miscarriage was relatively late in pregnancy, your HCG levels remain elevated for a while. This can cause a false positive test.
If you get a positive test result, even if you think it might be false, contact your doctor. Your doctor can assess HCG levels and determine whether you are pregnant. Early prenatal care can also reduce the risk of pregnancy complications and help you have a healthy pregnancy.
What to Do for a Suspected False Negative Test
The two-week wait can be agonizing. You might spend your time noticing every twinge and sensation, wondering if it might be a sign of pregnancy. Most women can’t resist the urge to take a pregnancy test as early as possible. But there’s no chance of a positive test before implantation. Implantation usually occurs sometime between seven and eleven days after ovulation.
If your first test is negative and you still think you might be pregnant, your best option is to wait a few days. HCG levels double rapidly, so the odds of a positive test just two days after a negative test are very high. If you can’t stand waiting, consider retesting later in the day with a more sensitive test. Home pregnancy tests usually reveal information about their sensitivity on the label, so read labels carefully and choose accordingly.
If you still get a negative test and don’t get your period, or if you just can’t stand waiting any longer, call your doctor. A blood test in a doctor’s office can detect even the lowest levels of HCG. What’s more, blood testing can analyze whether your HCG levels are normal and rising properly. This is an important fertility measure, especially for women with a prior history of chemical pregnancies or early miscarriage.
Signs of Infertility and When to See a Fertility Specialist
Trouble getting pregnant can make you feel as though you’ve lost control over your life and your body. Yet many people who struggle with infertility are reluctant to seek help. They worry that treatment will be too expensive, or that it won’t work, or that seeing a fertility specialist is a sign of defeat. The truth is that a fertility specialist is your best ally in the agonizing struggle of infertility. These fertility experts are much more knowledgeable than your gynecologist or family physician. That means you won’t waste time or effort on fertility treatment strategies that are doomed to fail. Instead, you’ll get a quick comprehensive workup and a treatment strategy designed for your life and values.
Most people with infertility have no symptoms other than difficulty getting pregnant. Yet some warning signs indicate a person might be at risk for infertility.
- Signs that the woman does not ovulate or ovulates infrequently, such as irregular periods.
- Ejaculatory or erectile dysfunction in the man.
- Swelling or pain in the man’s penis or testicles.
- A history of severe, chronic, or untreated infections, particularly STIs or STDs.
- A previous history of infertility in either partner, even if with a different partner.
- The woman is over the age of 35, or the man is over the age of 40.
- Very little semen in the man’s ejaculate.
- Symptoms of endometriosis, such as heavy or clotted periods.
- Symptoms of polycystic ovary syndrome (PCOS), such as unusual facial hair growth, unexplained weight gain, or insulin resistance.
Seeing a doctor before you begin trying can increase your odds of getting pregnant, especially if you have warning signs of infertility.
We also recommend seeing a specialist if:
- You have tried for a baby for longer than a year, and the woman is under 35.
- You have tried for a baby for longer than six months, and the woman is over 35.
- The woman has had two or more miscarriages in a row.
The Center of Reproductive Medicine, in Houston, Texas, understands the deep pain of infertility. We offer compassionate support in a private and judgment-free space. We work with you to understand your treatment goals and budget. And then identify treatment strategies consistent with your values, goals, and needs. For most patients, we are able to find a path to parenthood.
There is hope. Don’t walk this painful road alone. We can help you. Call one of our Texas fertility center locations today and we'll help you chart a course to parenthood. We’re standing by and ready to listen.