False Positive Pregnancy Test and Other Surprising Pregnancy Scenarios

By Bonnie Steele. Medically reviewed by Tom Iarocci, MD. May 7th 2016

Mississippi mom Kimberly Fugate was scheduled to give birth to identical triplets via cesarean section, but after delivering her three newborn daughters, the 42-year-old mom — and her doctors — were in for a surprise. Another sibling was waiting in the womb. The fourth baby had gone undetected in numerous ultrasounds throughout the pregnancy.

Surprises are more common than you might initially expect when it comes to multiple pregnancies, says Daniel Roshan, M.D., a New York-based OB-GYN who specializes in high-risk pregnancy and maternal fetal medicine. He explains that an embryo may split into two, giving rise to identical twins. Babies also constantly move around in their gestational sacs, so they may remain hidden behind one of their siblings during an ultrasound.

Yet, not all unexpected maternity tales occur in the delivery room. The first affirmation that you’re pregnant most often comes from a home pregnancy test. These early predictors are not 100 percent accurate, however. Follow up with a visit to your OB-GYN, especially if you’re experiencing symptoms that don’t mirror the test result.

Surprise #1: False-Negative Pregnancy Test

The test results said you’re not pregnant, but you’re nauseous, have swollen breasts and just feel different. There’s a chance your “negative” test results came back wrong, especially in certain circumstances:  

  • You took the test too early in the pregnancy. Pregnancy tests look for human chorionic gonadotropin (hCG) in your urine. Outer cells of the embryo begin to secrete hCG when implantation in the uterus occurs — usually seven to 10 days post ovulation. If you took the test prior to that time frame, there may not be enough hCG in your urine yet for an adequate reading.
  • Your urine is too diluted. Take the pregnancy test again using the first morning urine, especially if you drink a lot of water during the day.
  • Your home pregnancy test is calibrated too low. Early in your pregnancy, your levels of hCG are still relatively low. Many home pregnancy tests are calibrated to detect 100 mIU/ml, which may be higher than your current hCG levels. For example, if you are just seven days post-ovulation and took a home pregnancy test calibrated to detect 100 mIU/ml, the test will be negative.

Surprise #2: False-Positives and Chemical Pregnancies

Your home pregnancy test came back positive, but you later discover you are, in fact, not pregnant. How could this have happened?

  • You are undergoing infertility treatment with hCG. The doctor may have given you an hCG trigger shot to induce ovulation, which leaves traces of hCG in your urine for up to two weeks. Wait 14 days for it to clear your system before taking the test again.
  • You have experienced a chemical pregnancy. Chemical pregnancy is an early type of miscarriage that occurs before the fifth week of gestation. You actually conceived, but the pregnancy didn’t progress to the clinical pregnancy stage, in which a gestational sac can be seen by an ultrasound.
  • Misinterpretation of the test result is another possibility. Sometimes an evaporation line is mistaken for a positive result. Certain drugs such as tranquilizers or anticonvulsants (i.e., antiepileptic drugs) may cause home pregnancy tests to produce false positive results.

Surprise #3: False Pregnancy Can Cause a Big Belly

A false pregnancy, which is called pseudocyesis, may actually produce weight gain, a swollen belly and nausea for both parents (i.e., not just mothers, but also the men involved), and can last for weeks or even months. Typically, a mother (or a couple) who has been battling infertility suffers many, if not all, symptoms of pregnancy — with the exception of an actual fetus. In a case of false pregnancy, no baby will be seen on the ultrasound, and there won't be any heartbeat. 

This rare condition occurs across all different ethnic, racial and socioeconomic groups. The cause is not clear, but doctors believe a woman’s brain misinterprets hormonal signals and symptoms such as menstrual irregularities and abdominal enlargement.

Next Steps

  • To ensure accuracy, doctors recommend waiting to take a home pregnancy test until after missing a period. According to Roshan, women are most likely to get pregnant around day 14 of their cycle, and while a pregnancy can then be detected as early as day 24 or 25, he suggests waiting five to 10 days after you’ve missed a period.
  • It’s understandable to be anxious. If you waited to take the test, but the test is negative and your period still doesn’t come, test again, says Roshan. Because hGC levels usually double about every two days during the first few weeks of pregnancy, waiting will ensure there’s enough hGC in your urine to properly detect a pregnancy.
  • If you have any symptoms that seem inconsistent with your home test results, it’s a good idea to get checked out. Certain pregnancy problems can result in abnormally low hCG levels.

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