It is possible for a pregnancy test to show a positive result in the morning but a negative result in the afternoon. This can happen for a few different reasons:
Lower hCG levels in the afternoon
Pregnancy tests detect the presence of human chorionic gonadotropin (hCG), which is a hormone produced during pregnancy. hCG levels rise steadily during the first few weeks of pregnancy. However, the levels can fluctuate throughout the day. Typically, hCG levels are highest in the morning when the urine is more concentrated. As you drink more fluids during the day, hCG becomes diluted in your urine. This means an afternoon test may not detect hCG if the levels have dipped below the test’s sensitivity threshold.
Testing too early
If you take a pregnancy test very early in the pregnancy, hCG levels may be still be below the test’s limit of detection. But as hCG rises rapidly in these early days, a test done with morning urine could pick up on the hormone while an afternoon test may not. This could result in a positive test in the morning and negative in the afternoon.
Defective test
On rare occasions, a defective pregnancy test can give an erroneous positive result. If you take another test from the same box later in the day and get a negative result, the first test may have been defective.
Testing errors
User errors could also lead to inconsistent test results. For example, if the proper testing procedures were not correctly followed, such as not collecting enough urine or reading the results outside the manufacturer’s recommended testing window.
When does hCG rise during pregnancy?
To understand why pregnancy test results can vary by time of day, it helps to look at how hCG levels rise during early pregnancy:
| Week of pregnancy | Approximate hCG level range (mIU/mL) |
|---|---|
| 3 weeks | 5 – 50 |
| 4 weeks | 50 – 500 |
| 5 weeks | 500 – 10,000 |
| 6 weeks | 10,000 – 100,000 |
As you can see, hCG levels start off very low following implantation. Levels then rapidly increase, doubling every 48-72 hours in the first few weeks.
Most pregnancy tests on the market today can detect hCG levels around 25 mIU/mL. Some more sensitive tests go as low as 10 mIU/mL. This means very early on, hCG levels may hover right around the detectability threshold. A bit more dilution in the afternoon could drop levels low enough to get a negative result.
How accurate are pregnancy tests based on time of day?
Studies have looked at whether testing time impacts accuracy of pregnancy test results:
Morning urine
– One study found that pregnancy tests were 98-99% accurate when using first morning urine. This urine is typically the most concentrated.
Afternoon/evening urine
– Using urine later in the day resulted in more false negatives, with accuracy dropping to around 97% in the afternoon and 95% in the evening.
Sensitivity by time of day
– In another study, the same pregnancy test detected hCG at a level of 5 mIU/mL in morning urine. But the threshold rose to 10 mIU/mL for afternoon urine and 40 mIU/mL for evening urine due to dilution effects.
So while pregnancy tests remain highly accurate at any time of day, using first morning urine offers the best chance of detecting low levels of hCG early on.
How to interpret inconsistent pregnancy test results
What if your pregnancy test is positive in the morning but negative later that day? Here are some tips:
1. Retest with morning urine
Repeat the test first thing the next morning. Morning urine is your best bet for an accurate reading.
2. Use a more sensitive test
Try a test rated at 10 mIU/mL sensitivity instead of 25 mIU/mL. The more sensitive test will be better at detecting lower hCG levels.
3. Give it a few days
If it is very early, hCG may still be rising to readily detectable levels. Test again in 2-3 days to give levels more time to increase.
4. See your doctor
Your doctor can do a quantitative blood test to measure your exact hCG concentration and see if it is rising appropriately. This can provide definitive answers.
Tips for most accurate home pregnancy test results
To help ensure consistency in your pregnancy test results:
Use first morning urine
The highest concentration of hCG in your urine will be first thing in the morning after a long sleep.
Limit fluid intake before testing
Avoid drinking large amounts of liquid in the hours before the test. This will prevent excess dilution of hCG.
Follow test instructions
Read and follow the test directions carefully every time you take a test. Failing to do so can impact results.
Choose a sensitive test
Opt for a test rated at 10-25 mIU/mL for early detection of pregnancy. These will turn positive sooner.
Wait the full reaction time
Don’t read results early. The full reaction time stated in the test instructions is needed to get an accurate result.
Test more than once
If you get unexpected or inconsistent results, take another test before concluding you are not pregnant.
When to see a doctor
See your doctor or healthcare provider if:
– You get multiple inconsistent pregnancy test results over the course of a few days
– Your period is late but pregnancy tests remain negative
– You have symptoms of pregnancy without a positive test result
Blood tests measuring quantitative hCG levels can provide more definitive answers about the possibility of pregnancy. Your doctor can help interpret any confusing pregnancy test results.
The bottom line
In summary, it is certainly possible for pregnancy test results to vary by time of day. This most often occurs very early in pregnancy when hCG is still rising and levels are borderline. While frustrating, inconsistent results are not uncommon. Retest with first morning urine and see your doctor if results remain unclear. With some patience and the right testing methods, you will eventually get an accurate read on your pregnancy status.