If you suspect you might be pregnant, you should take a home pregnancy test the day of your expected period, preferably in the morning. If the test is negative, it is best to take another test 1 week after a missed period or about 3 weeks after unprotected sex to avoid a false-positive or false negative result.
What do pregnancy tests look for?
During a normal 28-day menstrual cycle, the following events occur::
- Ovulation: Mature egg is released from an ovary; occurs around day 15.
- Fertilization: Egg is fertilized by sperm.
- Implantation: Resulting embryo travels to the uterus (womb) and implants itself in the uterine wall; occurs 6-9 days after fertilization.
- Human chorionic gonadotropin (hCG) production: At this stage, a tiny amount of hCG (pregnancy hormone) is produced by the cells that later form the placenta and appears in the urine; occurs about 10 days after conception.
Pregnancy tests detect the presence of hCG hormone in either urine or blood:
- Urine tests: Performed at home and can detect hCG approximately 12-15 days post ovulation
- Blood tests: Can provide accurate results far earlier in pregnancy:
- Qualitative hCG: Detects the presence or absence of hCG as early as 10 days after conception
- Quantitative hCG: Measures the amount of hCG in a blood sample
How does a home pregnancy test work?
Home pregnancy tests are simple to use, reliable, almost 99% accurate, inexpensive, available over the counter, and provide results within 5 minutes if done properly.
A typical home pregnancy test involves testing urine on a chemical strip, which reacts to the amount of hCG in the urine. Different brands vary in the methods used to collect or test urine and the way the results are produced. Results may be revealed by:
- Indicator lines (1-2 lines)
- Digital terms (“pregnant” or “not pregnant”)
- Signs (+ or -)
Follow all the instructions on the kit and read the results within 5 minutes. Waiting longer than 10-20 minutes may lead to inaccurate results.
Is there any way a pregnancy test can be wrong?
Although pregnancy tests claim to be 99% accurate, there is still a chance of getting a false-negative or false-positive result.
Factors that can lead to a false-negative result include:
- Diluted urine
- Testing too soon
- Delayed implantation
- Wrong or miscalculation of period due date
- Irregular menstrual cycles
Factors that can lead to a false-positive result include:
- Chemical pregnancy
- Miscarriage (early pregnancy loss)
- Ectopic pregnancy (pregnancy that develops outside the uterus)
- Certain medications such as fertility treatments (clomiphene and menotropins), birth control pills, carbamazepine, and methadone
- Medical conditions such as ovarian cysts, ovarian cancer, breast cancer, bladder cancer, and kidney diseases
- Molar pregnancy (a rare complication of pregnancy characterized by tumor growth in the uterus)
- Expired kits
- Evaporation line (a faint line appearing in the test window caused by urine evaporation)
What are early signs of pregnancy?
Significant hormonal changes occur in the body during pregnancy that may trigger symptoms such as:
Health Solutions From Our Sponsors
Pregnancy Tests. Cleveland Clinic: https://my.clevelandclinic.org/health/articles/9703-pregnancy-tests
Pregnancy tests. Office on Women’s Health: https://www.womenshealth.gov/a-z-topics/pregnancy-tests
Human Chorionic Gonadotropin. University of Michigan: https://www.uofmhealth.org/health-library/hw42062