How Medications Can Effect Pregnancy Test Results

Fertility treatments may lead to a false positive reading

Pregnancy Test

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Home pregnancy tests work by detecting the presence of human chorionic gonadotropin (hCG) in a urine sample. There are a few things that can cause a false negative reading, namely the improper use of the test, testing too early, using an expired test, or diluting the urine by drinking too much water in advance.

There are also a few medications that can interfere with the result. Rather than triggering a false negative, they can sometimes return a false positive reading, leading to you believe that you are pregnant when, in fact, you are not.

Types of hCG Preparations

For women undergoing in vitro fertilization (IVF) or intrauterine insemination (IUI), there are drugs used in the process that can interfere with hCG levels because they are hCG.

For women unable to ovulate on their own, a fertility medication such as Clomid (clomiphene citrate) may be prescribed to induce ovulation. After completing the five-day course, a "trigger" injection of Pregnyl, Ovidrel, or Novarel may be delivered to complete maturation and release the egg.

Pregnyl, Ovidrel, and Noveral are all brand name preparations of hCG. When using these drugs, you would need to wait at least two weeks before getting tested so that the injected hCG can be fully cleared from the body. If not, you risk a false reading.

Even then, most doctors will advise against home testing and ask that you come to the office to get a blood-based beta test. While the beta test also detects for hCG, it is far more accurate than a home urine-based test.

Types of hMG Preparations

Another type of injectable drug, known as human menopausal gonadotropin (hMG), can be used to aid in ovulation. Also known as menotropin, the injection is comprised of a mixture of luteinizing hormone (LH) and follicle stimulating hormone (FSH).

When used for IVF or IUI, the LH component can also trigger a false positive result but for different reasons. While an hCG injection causes false positive by introducing hCG into the system, a surge in LH can do the same because the two hormones are so genetically similar.

A list of approved hMG preparations include:

  • Gynogen HP
  • HMG Massone
  • Humog
  • Humegon
  • Menopur
  • Merional
  • Menogon
  • Metrodin
  • Pergonal
  • Repronex

If You Believe Your Pregnancy Test Is Wrong

If you've taken a pregnancy test and believe that a negative result is wrong, the best thing to do is wait for a least two days and test again. Oftentimes, if you test too early, the hCG levels will be below the threshold of detection of many home pregnancy tests.

By waiting two days, your hCG levels will usually double if you are pregnant. If you wait another two days, the levels will double again, increasing your chance of an accurate reading.

If, on the other hand, you are undergoing IVF or IUI, it is best to follow your doctor's instructions and wait to get an in-office beta test. While having to wait two weeks can add anxiety to an already emotional process, you risk bigger heartbreak if you get a positive reading that turns out to be untrue.

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Article Sources
  • Kaiser, U. "Chapter 7 – Gonadotrophin Hormones." (2017) The Pituitary (Fourth Ed.) Cambridge, Massachusetts: Academic Press. DOI: 10.1016/B978-0-12-804169-7.00007-6.
  • Orvieto, R. "Triggering final follicular maturation- hCG, GnRH-agonist or both, when and to whom?" J Ovarian Res. 2015; 8:60. DOI: 10.1186/s13048-015-0187-6.