Can Hormones Affect Pregnancy Test Results?

Pregnancy tests work by detecting the presence of human chorionic gonadotropin (hCG), a hormone produced during pregnancy, in a woman’s urine or blood. This leads many women to wonder – can hormones other than hCG affect pregnancy test results? The short answer is yes, certain hormones can impact the accuracy of pregnancy tests.

How Pregnancy Tests Work

Pregnancy tests detect hCG, which is produced by the placenta shortly after implantation occurs. Levels of hCG rise steadily during the first trimester. Most at-home urine pregnancy tests can detect hCG levels above 25 mIU/mL. The threshold for a positive result varies by brand, but is typically between 25-50 mIU/mL.

Blood tests administered by a doctor are even more sensitive than urine tests, able to detect hCG levels as low as 5-10 mIU/mL. The high sensitivity of blood tests makes them useful for detecting pregnancy sooner.

When taking a pregnancy test, timing is important. Blood and urine tests are most accurate when taken after a missed period. Testing too early can lead to a false negative result. Levels of hCG may not yet be high enough for the test to detect.

How Hormones Can Affect Pregnancy Test Results

HCG is not the only hormone present in a woman’s body. Fluctuating levels of other hormones can impact pregnancy testing results.


Progesterone helps prepare the uterus for pregnancy. Birth control pills contain synthetic progesterone to prevent ovulation. High progesterone from birth control or hormone therapy can lead to false positive pregnancy test results.

Follicle Stimulating Hormone (FSH)

FSH regulates ovulation and stimulates egg production. Elevated FSH levels are associated with perimenopause and menopause. As fertility declines, high FSH may cause inaccurate pregnancy test results.

Luteinizing Hormone (LH)

LH triggers ovulation. An LH surge before ovulation can mimic rising hCG levels, leading to a false positive on some pregnancy tests. Certain fertility medications also contain hCG or LH.

Human Growth Hormone (HGH)

HGH helps regulate growth, metabolism and reproduction. Therapeutic use can skew pregnancy test results. High HGH levels may register as a false positive.

Thyroid Hormone

Thyroid hormones T3 and T4 impact menstrual cycles and fertility. Both hypothyroidism and hyperthyroidism can interfere with ovulation and cause irregular periods, complicating accurate testing.


Oestrogen works with other hormones to control the menstrual cycle. Very high estrogen levels can potentially cause a false positive pregnancy test. Conditions like ovarian cysts can increase oestrogen.

Evaporation Lines

Evaporation lines may also be mistaken for a positive pregnancy test result. After taking the test, the urine saturates the result area. When the urine evaporates, a faint line may appear where the positive result should be. Evaporation lines can look similar to a positive result but indicate a negative test.

Avoiding Inaccurate Results

While it is possible for hormones to interfere with pregnancy test accuracy, there are steps women can take to avoid false results:

– Take the test first thing in the morning, when hCG levels are most concentrated
– Do not take a urine test until after a missed period
– Follow all test instructions carefully
– Check results within the manufacturer’s recommended time frame
– Do not interpret very faint lines as a positive result
– Retest with a blood test if uncertain

The most reliable way to determine pregnancy status is through laboratory quantitative hCG blood testing. While at-home urine tests provide a convenient option, women concerned about accuracy may want to confirm with their healthcare provider. Testing too early, improper test use, and certain medical conditions can all increase the chances of incorrect results. When used properly, modern pregnancy tests are highly accurate. However, unexpected hormones may still impact the outcome in some cases. Consulting a doctor can provide definitive answers if pregnancy test results remain unclear.

Potential Causes of Inaccurate Results

Hormonal fluctuations happen routinely throughout the menstrual cycle and can impact pregnancy testing if not properly timed. However, certain medical conditions or medications may also affect accuracy:

  • Polycystic Ovarian Syndrome (PCOS)Women with PCOS have chronic hormone imbalances. Elevated LH levels mimic HCG, while low progesterone mimics early pregnancy. This can increase chances of false positives.
  • Ovarian Tumours – Tumours may secrete HCG, leading to a false positive test. Or they can suppress normal ovarian function and ovulation. Lack of ovulation reduces progesterone, potentially also causing inaccurate results.
  • Perimenopause/Menopause – Declining ovarian function affects progesterone and oestrogen levels. Menstrual irregularity makes timing difficult. Low fertility increases chances of false negatives.
  • Hormone Replacement Therapy – HRT used to treat perimenopause and menopause symptoms may contain estrogen, progesterone or HCG. This can interfere with accurate testing.
  • Fertility Drugs – Ovulation induction medications use hormones like clomiphene, gonadotropins and HCG to stimulate ovulation. Multiple eggs and hormonal fluctuations complicate testing.
  • Recent Birth Control – Post-pill amenorrhea means no menses to date from. Residual synthetic hormones may also be present. Both increase odds of erroneous results.
  • Breastfeeding – Lactation suppresses ovulation and menstruation. Low estrogen/progesterone levels paired with persistent HCG from pregnancy can confuse tests.
  • Medications – Certain antipsychotics, hypertension and diabetes drugs have hormonally active components. Consult a doctor regarding potential interactions.

When to Retest

If unsure of results, repeat testing is advisable:

  • Wait 1 week after first test, then retest with first morning urine
  • Ensure no fluids for 4 hours prior, to concentrate HCG
  • If still unclear, test again 1 week later to allow more time for HCG rise
  • Get quantitative bloodwork for a definitive answer
  • Discuss medications with doctor, schedule test 3-5 days after ending hormones
  • Time test just before expected period if irregular cycles
  • Use as directed and read during timeframe specified

Retesting with a sensitive blood test can provide the most accurate answer when uncertainty remains. Home urine testing works best when followed precisely. Being aware of what impacts results allows proper action to avoid false positives or negatives. While hormones can potentially interfere, sticking to best practices helps pregnancy tests give reliable outcomes in most normal circumstances.

Photo by Anthony Cunningham for Zoom Baby

Zoom Baby is a leading supplier of Pregnancy Tests and Ovulation Test Kits

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