Home pregnancy tests are a common tool used to find out if you’re expecting. Most at-home pregnancy tests are dipsticks that are placed in a urine stream. The stick is then able to detect human chorionic gonadotropin (hCG), which is a hormone produced during early pregnancy.
Some pregnancy tests detect hCG very early in pregnancy. Reputable home pregnancy tests can be highly accurate, but they are not foolproof.
False-positive and false-negative tests can occur for a variety of reasons. It’s also important to remember that once you have a positive pregnancy test, it’s important to talk with your doctor about beginning early prenatal care.
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1. Chemical pregnancy
It’s possible to have a positive pregnancy test even if you aren’t technically pregnant. This is called a false positive.
It’s sometimes caused by a chemical pregnancy. A chemical pregnancy occurs if a fertilized egg, known as the embryo, is unable to implant, or grow, very early on. This can happen for many reasons.
Some causes of chemical pregnancies are unknown.
They are thought to be very common, but they typically go undetected if a pregnancy test isn’t taken. These early test results, when wrong, can be emotionally draining.
For that reason, it’s recommended you wait until 1 week after you expected your period to start to use an at-home pregnancy test.
2. Ectopic pregnancy
Sometimes a fertilized egg can implant itself outside of the main cavity of the uterus, which causes an ectopic pregnancy. An ectopic pregnancy is a serious medical emergency and must be addressed immediately.
Ectopic pregnancies usually happen if a fertilized egg gets stuck in a fallopian tube during its journey to the uterus. This type of ectopic pregnancy is also known as a tubal pregnancy.
An ectopic pregnancy can just happen, but risk factors include:
- scar tissue or inflammation in the fallopian tube
- misshapen fallopian tube or other congenital anomalies
- a history of infertility treatments such as in vitro fertilization (IVF)
- a history of uterine or tubal surgery
- a history of past uterine infections
- a history of a prior ectopic pregnancy
- Ectopic pregnancies can also occur in the cervix, ovary, or abdominal cavity.
An ectopic pregnancy is a medical emergency. It can’t continue to become a normal pregnancy and it can be damaging to the woman if left untreated. The embryo isn’t viable because there’s no place for it to grow or thrive outside of the uterus.
Extreme blood loss or loss of the reproductive organs can occur. Bleeding and pain in early pregnancy need to be evaluated by a medical professional immediately.
The embryo will still produce hCG, even though it has been implanted in the wrong place. That can cause a false-positive reading on an at-home pregnancy test.
Symptoms of ectopic pregnancy include:
- sharp waves of pain in the abdomen, pelvis, shoulder, or neck
- severe pain on one side of the abdomen
- light to heavy vaginal spotting or bleeding
- dizziness or fainting
- pressure on your rectum
Seek immediate medical help if you suspect you have an ectopic pregnancy.
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3. Recent miscarriage or abortion
You may continue to test positive for pregnancy following the loss of a pregnancy, either through miscarriage or abortion.
During pregnancy, the hCG levels continue to rise, in general doubling every few days and peaking at around 10 weeks. This is before the placenta is formed and functional around week 12.
The hormone can remain in your blood and urine for up to 6 weeks following the end of the pregnancy. It’s possible to have a false-positive test until your hCG levels return to their pre-pregnancy state.
If the miscarriage was spontaneous, it’s also possible that not all the pregnancy-related tissue was eliminated. This can cause hCG levels to remain elevated, among other more worrisome symptoms such as ongoing bleeding or fever.
An ultrasound is generally needed to determine if an intrauterine pregnancy is identified, or lost, or if there is a fetus without cardiac activity.
When this occurs, sometimes a minor surgical procedure called a dilation and curettage (D and C) is often required to remove the tissue, depending upon your symptoms and how far along the pregnancy was.
4. User error
At-home pregnancy tests aren’t foolproof. It’s important to follow package directions exactly. Check the expiration date before using the test.
Even with these safeguards, user error can occur. One of the most common mistakes is taking the test too early during your cycle. This can cause either a false negative or a false positive
It’s also important to use the test when your urine isn’t diluted excessively with water. Use the test when your urine is very concentrated, like when you first wake up in the morning.
Leaving the dipstick in your urine stream for the exact amount of time allotted is also important. Consider setting a timer on a stopwatch or your phone. That can help you track how long the dipstick has been in your urine stream.
You’ll want to use a timer again while you wait for your results. Checking your results during the result time frame is also important.
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5. Evaporation lines
Sometimes an evaporation line can be mistaken for a positive pregnancy test. Some at-home tests show two lines when hCG is detected and one line when hCG isn’t detected.
The lines are usually bright colors, such as pink, red, or blue. Sometimes, a faint-colored second line will appear. This line may represent an early pregnancy, or it may be an evaporation line.
It’s probably an evaporation line if the line is completely colorless.
Evaporation lines may show up on a test you view after your urine has evaporated completely. Sometimes they’re caused by hormonal levels that don’t represent pregnancy.
The best way to try and prevent being confused by an evaporation line is to follow the test’s timing directions exactly as they’re given.
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6. Medications
If you’re trying to become pregnant under a doctor’s care, you may be taking fertility medications.
One of these is the synthetic hCG trigger shot, sold under the following brand names:
- Novarel
- Pregnyl
- Ovidrel
- Profasi
The hCG shot helps follicles release mature eggs. It may cause a false-positive reading on an at-home pregnancy test, particularly if the test is taken too early.
Other medications can also cause false-positive pregnancy tests. They include but aren’t limited to:
- anti-anxiety medications, like diazepam (Valium) or alprazolam (Xanax)
- antipsychotics, such as clozapine or chlorpromazine
- anticonvulsants, like phenobarbital or other barbiturates
- Parkinson’s disease medications, including bromocriptine (Parlodel)
- diuretics, like furosemide (Lasix, Diuscreen)
- antihistamines, including promethazine
- methadone (Dolophine)
7. Certain medical conditions
Rarely, certain medical conditions can cause a home pregnancy test to give a false positive. These include:
- molar pregnancy
- rare antibodies
- hydroxychloroquine (HCQ) injections
- chemotherapy
- urinary tract infection
- kidney disease that causes blood or white blood cells in the urine
- germ cell tumors of the ovary, a type of ovarian cancer
- pituitary problems (very rarely)
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Next steps
A positive at-home pregnancy test result should always be followed up with a doctor’s appointment. Your doctor may give you a urine or blood test to confirm the results and monitor your hCG levels.
They may also order a transvaginal ultrasound to confirm that the pregnancy is proceeding normally. A follow-up ultrasound may be needed after about 1 week — if it’s early — to verify the results.
If you’ve received a false positive, your doctor’s visit will determine that. Depending on your situation, it might be a relief to find out you’re not pregnant.
But if you were excited by your early results, it can be very upsetting. Remember that false positives do happen and are not an indication that you cannot become pregnant in the future.
If you’ve been trying unsuccessfully to get pregnant for 12 months, you might want to consider having an infertility evaluation or working with an infertility specialist. Women ages 35 and olderTrusted Source who have been trying unsuccessfully to get pregnant for 6 months are recommended to seek an infertility evaluation.
There are support groups where you can find inspiration and obtain knowledge from women who have been through the same thing.
Working one-on-one with a therapist, family member, or trusted friend can also be beneficial.